全文获取类型
收费全文 | 5504篇 |
免费 | 98篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 28篇 |
综合类 | 9篇 |
化学工业 | 536篇 |
金属工艺 | 73篇 |
机械仪表 | 90篇 |
建筑科学 | 74篇 |
矿业工程 | 8篇 |
能源动力 | 209篇 |
轻工业 | 379篇 |
水利工程 | 22篇 |
石油天然气 | 26篇 |
无线电 | 147篇 |
一般工业技术 | 493篇 |
冶金工业 | 3182篇 |
原子能技术 | 36篇 |
自动化技术 | 306篇 |
出版年
2024年 | 10篇 |
2023年 | 43篇 |
2022年 | 86篇 |
2021年 | 104篇 |
2020年 | 99篇 |
2019年 | 97篇 |
2018年 | 130篇 |
2017年 | 125篇 |
2016年 | 111篇 |
2015年 | 77篇 |
2014年 | 88篇 |
2013年 | 223篇 |
2012年 | 149篇 |
2011年 | 153篇 |
2010年 | 113篇 |
2009年 | 144篇 |
2008年 | 155篇 |
2007年 | 112篇 |
2006年 | 81篇 |
2005年 | 65篇 |
2004年 | 47篇 |
2003年 | 47篇 |
2002年 | 27篇 |
2001年 | 15篇 |
2000年 | 20篇 |
1999年 | 126篇 |
1998年 | 1031篇 |
1997年 | 609篇 |
1996年 | 380篇 |
1995年 | 181篇 |
1994年 | 192篇 |
1993年 | 193篇 |
1992年 | 36篇 |
1991年 | 24篇 |
1990年 | 27篇 |
1989年 | 29篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 25篇 |
1981年 | 23篇 |
1980年 | 22篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 87篇 |
1976年 | 163篇 |
1975年 | 4篇 |
排序方式: 共有5618条查询结果,搜索用时 15 毫秒
951.
VM Reddy DB McElhinney MM Brook AJ Parry FL Hanley 《Canadian Metallurgical Quarterly》1998,115(5):1032-1040
BACKGROUND: Though repair of complete atrioventricular septal defect in infancy has become routine at most centers, it is not unusual for very young infants to be managed medically because of concerns about the fragility of the atrioventricular valve tissue. METHODS: Since July 1992, seventy-two infants have undergone primary repair of complete atrioventricular septal defects at a median age of 3.9 months (40% < 3 months). A single-patch technique was used in all patients. The cleft was closed completely in 61 patients and partially (n = 10) or not at all (n = 1) in select patients at risk for valve stenosis. Left atrioventricular valve annuloplasty was performed in 18 patients. On the basis of transesophageal echocardiographic findings, 10 patients were returned to bypass for revision of the valve repair. RESULTS: There was one early death in a patient with single left papillary muscle, no early reoperations, and no new permanent arrhythmias. Only three patients had moderate left atrioventricular valve regurgitation at discharge. During a median follow-up of 24 months, there was one late death and five reoperations for left atrioventricular valve regurgitation (n = 2) and/or systemic outflow obstruction (n = 4). Follow-up left atrioventricular valve regurgitation was moderate in three patients, mild in 14, and none/trace in 54. Age had no relation to postoperative atrioventricular valve regurgitation, death, or reoperation. CONCLUSIONS: Despite concerns about fragility of valve tissue in very young patients, excellent results can be achieved with meticulous techniques. From neonates to older infants, age at repair does not influence outcome or valve function. 相似文献
952.
G Ntirampemba BE Langlois DD Archbold TR Hamilton-Kemp MM Barth 《Canadian Metallurgical Quarterly》1998,61(10):1352-1357
OBJECTIVE: The authors tested the hypothesis that eye tracking disorder in schizophrenia is associated with neurological signs. METHOD: The subjects were 93 normal comparison subjects and 59 schizophrenic patients. They were evaluated with the Neurological Evaluation Scale, a standardized rating instrument that assesses sensory integration, motor coordination, sequencing of complex motor acts, and other neurological signs. Also, the schizophrenic patients' smooth-pursuit eye movements were tested in response to a 0.3-Hz sinusoidal target by means of infrared oculography. They were divided into those with (N=18) and without (N=41) eye tracking disorder by using a previously described method, which was based on mixture analysis of the distribution of position root mean square error. RESULTS: The patients with eye tracking disorder had significantly worse performance than the patients without eye tracking disorder with respect to sensory integration, and the effect size was moderate to large. In comparison with the normal subjects, both patient subgroups had significantly worse performance on all of the Neurological Evaluation Scale subscales. CONCLUSIONS: Although neurological signs are present generally in schizophrenia, poor sensory integration is particularly pronounced in patients with eye tracking disorder. A review of the literature shows that the two abnormalities have strikingly similar patterns of validators, including 1) familial aggregation, 2) premorbid presence, 3) syndromal specificity, 4) trait status, and 5) association with the deficit syndrome. Poor sensory integration and eye tracking disorder in schizophrenia may be various manifestations of a common, underlying pathophysiological process. 相似文献
953.
GK Lloyd F Menzaghi B Bontempi C Suto R Siegel M Akong K Stauderman G Velicelebi E Johnson MM Harpold TS Rao AI Sacaan LE Chavez-Noriega MS Washburn JM Vernier ND Cosford LA McDonald 《Canadian Metallurgical Quarterly》1998,62(17-18):1601-1606
Neuronal nicotinic acetylcholine receptors (NAChRs) are pentameric ligand-gated ion channel receptors which exist as different functional subunit combinations which apparently subserve different physiological functions as indicated by molecular biological and pharmacological techniques. It is possible to design and synthesize novel compounds that have greater selective affinities and efficacies than nicotine for different NAChRs, which should translate into different behavioral profiles and therapeutic potentials. Examples of NAChR agonists studied are nicotine, SIB-1508Y, SIB-1553A and epibatidine. These compounds have different degrees of selectivity for human recombinant NAChRs, different neurotransmitter release profiles in vitro and in vivo and differential behavioral profiles. Preclinical studies suggest that SIB-1508Y is a candidate for the treatment of the motor and cognitive deficits of Parkinson's disease, whereas SIB-1553A appears to have potential as a candidate for the treatment of Alzheimer's disease. Epibatidine has a strong analgesic profile, however the ratio between pharmacological activity and undesirable effects is so low that it is difficult to envisage the use of this compound therapeutically. Nicotine has a broad profile of pharmacological activity, for instance demonstrating activity in models for cognition and analgesia. As for epibatidine, the adverse effects of nicotine severely limits its therapeutic use in humans. The discovery of subtype-selective NAChR agonists such as SIB-1508Y and SIB-1553A provides a new class of neuropsychopharmacological agents with better therapeutic ratios than nonspecific agents such as nicotine. 相似文献
954.
Little is known about the stability of fumonisins in corn-based foods during heating. This study investigated the effects of canning, baking, and roasting (dry heating) processes on the stability of fumonisins in artificially contaminated and naturally contaminated corn-based foods. All samples were analyzed for fumonisin levels by both a commercial enzyme-linked immunosorbent assay (ELISA) and a high-performance liquid chromatographic (HPLC) method. Canned whole-kernel corn showed a significant (P < or = 0.05) decrease in fumonisins by both ELISA (15%) and HPLC (11%) analyses. Canned cream-style corn and baked corn bread showed significant (P < or = 0.05) decreases in fumonisin levels at an average rate of 9% and 48%, respectively, as analyzed by ELISA. Corn-muffin mix artificially contaminated with 5 micrograms of fumonisin B1 (FB1) per g and naturally contaminated corn-muffin mix showed no significant (P < or = 0.05) losses of fumonisins upon baking. Roasting cornmeal samples artificially contaminated with 5 micrograms of FB1 per g and naturally contaminated cornmeal samples at 218 degrees C for 15 min resulted in almost complete loss of fumonisins. 相似文献
955.
The -514 polymorphism in the hepatic lipase gene (LIPC) is associated with decreased hepatic lipase activity. In the present study, the interaction between body mass index (BMI), the -514 polymorphism, and hepatic lipase activity was examined in 118 white men and in 51 African American men. BMI was significantly positively correlated with hepatic lipase activity in both populations. BMI was similar in men with genetic differences in hepatic lipase activity, indicating that high hepatic lipase activity did not cause increased BMI. The data therefore suggest that high BMI leads to increased hepatic lipase activity. The actions of BMI and the -514 polymorphism on hepatic lipase activity appear to be additive and independent, rather than synergistic. This finding indicates that hepatic lipase activity is a multifactorial trait, determined in part by polymorphism within the LIPC gene as well as by factors that influence BMI. 相似文献
956.
MS Prachand MM Dhingra A Saran E Coutinho J Bodi H Süli-Vargha K Medzihardszky 《Canadian Metallurgical Quarterly》1998,51(4):251-265
Solution conformation of cyclo(Gly1-His2-Phe3-Arg4-Trp5-Gly6) and its D-Phe analog corresponding to the message sequence [Gly-alpha-MSH5-10] of alpha-MSH has been studied by 1D and 2D proton magnetic resonance spectroscopy in dimethyl sulfoxide (DMSO)-d6 solution and in a DMSO-d6/H2O cryoprotective mixture. The NMR data for both the analogs in solution at 300 K cannot be interpreted based on a single ordered conformation, as evidenced by the broadening of only -NH resonances as well as the temperature coefficients of the amide protons. An analysis of the nuclear Overhauser effect (NOE) cross-peaks in conjunction with temperature coefficient data indicates an equilibrium of multiple conformers with a substantial population of particular conformational states at least in the D-analog. The molecular dynamics simulations without and with NOE constraints also reveal numerous low-energy conformers with two gamma-turns, a gamma-turn and a beta-turn, two beta-turns, etc. for both the analogs. The observed NMR spectra can be rationalized by a dynamic equilibrium of conformers characterized by a gamma-bend at Gly6, two gamma-bends at Phe3 and Gly6 and a conformer with a single beta-turn and a gamma-bend for the L-Phe analog. On the other hand, a conformation with two fused beta-turns around the two tetrads His2-D-Phe3-Arg4-Trp5 and Trp5-Gly6-Gly1-His2 dominates the equilibrium mixture for the D-Phe analog. For the D-Phe analog, the experimentally observed average conformation is corroborated by molecular dynamics simulations as well as by studies in cryoprotective solvent. 相似文献
957.
JJ Claus I de Koning F van Harskamp MM Breteler B Voet H Gutzmann F Dahlke T van der Cammen A Hofman 《Canadian Metallurgical Quarterly》1998,21(3):190-195
The approach to nasal bone classic corrective rhinoplasty is an almost-blind technique, where the results depends on feeling by the surgeon's hand. To overcome these drawbacks, endoscopic-assisted corrective rhinoplasty and septoplasty were performed for 16 cases of deviated noses between January 1995 and May 1997. The average follow-up period was 18 months. All patients were evaluated by symmetrical nasal pyramid, recurrence of the bony deflection, and septal deviation. The postoperative courses were satisfactory in most cases, with few complications. Compared with 28 cases of classic rhinoplasty, the patient satisfaction rate was high (87.5% in endoscopic-assisted rhinoplasty, 71.4% in classic rhinoplasty), and the complication and revision rate was low (0% in endoscopic-assisted rhinoplasty, 14.3 and 7.1% in classic rhinoplasty). But extra time (about 40 min) and greater expense were required for endoscopic-assisted rhinoplasty. It appeared to us that endoscopic control during corrective rhinoplasty and septoplasty is a big step toward obtaining better results in bony and cartilage resection with extreme precision under monitor control and magnification. This technique is not an open approach but permits one to see more of the nasal skeleton and bony septum, the cause of the deformity, and the immediate effect of the corrective measures used. The use of an endoscope in corrective rhinoplasty for deviated noses provides an expanded field of vision, direct manipulation of lesions, and better aesthetic and functional results. 相似文献
958.
MM Graham LM Peterson M Muzi BB Graham AM Spence JM Link KA Krohn 《Canadian Metallurgical Quarterly》1998,39(10):1805-1810
1-[Carbon-11]-D-glucose ([11C]-glucose) is an important imaging agent for PET studies that have been used to study the normal brain, encephalitis, epilepsy, manic-depressive disorder, schizophrenia and brain tumors. METHODS: Dosimetry estimates were calculated in subjects undergoing imaging studies to help define the radiation risk of [11C]-glucose PET imaging. Time-dependent radioactivity concentrations in normal tissues in 33 subjects after intravenous injection of [11C]-glucose were obtained by PET imaging. Radiation absorbed doses were calculated according to the procedures of the Medical Internal Radiation Dose (MIRD) committee along with the variation in dose based on the calculated standard deviation of activity distribution seen in the individual patients. RESULTS: Total body exposure was a median of 3.0 microGy/MBq in men and 3.8 microGy/MBq in women. The effective dose equivalent was 3.8 microGy/ MBq in men and 4.8 microGy/MBq in women. The critical organs were those that typically take up the most glucose (brain, heart wall and liver). CONCLUSION: The organ doses reported here are small and comparable to those associated with other commonly performed nuclear medicine tests and indicate that potential radiation risks associated with this radiotracer are within generally accepted limits. 相似文献
959.
The inferior frontal gyrus has traditionally been considered an important cortical region for language and may be important for understanding developmental language disorders. The morphology of the inferior frontal gyrus, as it appeared on T1-weighted sagittal magnetic resonance imaging (MRI) scans, was evaluated using a classification system that distinguished between seven basic morphological variants of the gyral and sulcal patterns in this region. This classification scheme was applied to the MRI scans of 41 neurologically normal adult subjects. To examine the relation between sulcal morphology and subject status, these subjects were sorted first by family history for developmental language disorders and then resorted by expression of behavioral signs consistent with a diagnosis of this disorder as determined by standardized testing. Morphological types that included an extra sulcus in the inferior frontal gyrus were statistically associated with the behaviorally based classification of subjects, but not with a positive family history for developmental language disorders. Because gyral patterns are prenatally determined, this finding is consistent with the theory that altered prenatal development contributes to the expression of a developmental language disorder. 相似文献
960.
The gene rafY from the plasmid pRSD2, which enables Escherichia coli to grow on raffinose, was transferred into expression plasmid pUSL77. The protein was expressed in the porin-deficient Escherichia coli strain KS26 and was isolated and purified to homogeneity. The pure protein was reconstituted into lipid bilayer membranes. It formed an ion-permeable channel with a single-channel conductance of 2.9 nS of the open state in 1 M KCl, which is approximately twice of that of the general diffusion pores OmpF and OmpC of E. coli outer membrane. At lower pH the channel exhibited rapid flickering between three substates of the open channel. The RafY channel appears to be wide and water filled and has a small selectivity for cations over anions. Although RafY is part of an uptake and fermentation system for raffinose it does not contain a binding site for carbohydrates. Our results suggest that RafY is a general diffusion pore with a diameter, larger than that of the general diffusion porins OmpF and OmpC, that allows the diffusion of high-molecular-mass carbohydrates through the outer membrane. 相似文献