全文获取类型
收费全文 | 10786篇 |
免费 | 107篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 98篇 |
综合类 | 2篇 |
化学工业 | 1015篇 |
金属工艺 | 103篇 |
机械仪表 | 303篇 |
建筑科学 | 216篇 |
矿业工程 | 28篇 |
能源动力 | 129篇 |
轻工业 | 872篇 |
水利工程 | 107篇 |
石油天然气 | 17篇 |
无线电 | 863篇 |
一般工业技术 | 1020篇 |
冶金工业 | 5268篇 |
原子能技术 | 109篇 |
自动化技术 | 753篇 |
出版年
2021年 | 69篇 |
2020年 | 51篇 |
2019年 | 61篇 |
2018年 | 61篇 |
2017年 | 82篇 |
2016年 | 66篇 |
2015年 | 47篇 |
2014年 | 104篇 |
2013年 | 315篇 |
2012年 | 160篇 |
2011年 | 238篇 |
2010年 | 213篇 |
2009年 | 231篇 |
2008年 | 260篇 |
2007年 | 240篇 |
2006年 | 246篇 |
2005年 | 219篇 |
2004年 | 178篇 |
2003年 | 200篇 |
2002年 | 201篇 |
2001年 | 162篇 |
2000年 | 160篇 |
1999年 | 252篇 |
1998年 | 1365篇 |
1997年 | 845篇 |
1996年 | 634篇 |
1995年 | 409篇 |
1994年 | 362篇 |
1993年 | 384篇 |
1992年 | 131篇 |
1991年 | 149篇 |
1990年 | 155篇 |
1989年 | 165篇 |
1988年 | 164篇 |
1987年 | 171篇 |
1986年 | 133篇 |
1985年 | 148篇 |
1984年 | 95篇 |
1983年 | 105篇 |
1982年 | 84篇 |
1981年 | 104篇 |
1980年 | 95篇 |
1979年 | 79篇 |
1978年 | 74篇 |
1977年 | 194篇 |
1976年 | 380篇 |
1975年 | 76篇 |
1974年 | 71篇 |
1973年 | 63篇 |
1972年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Johnson R.A. de la Houssaye P.R. Chang C.E. Pin-Fan Chen Wood M.E. Garcia G.A. Lagnado I. Asbeck P.M. 《Electron Devices, IEEE Transactions on》1998,45(5):1047-1054
This paper reviews the prospects of thin-film silicon-on-sapphire (TFSOS) CMOS technology in microwave applications in the 1-5 GHz regime and beyond and presents the first demonstration of microwave integrated circuits based on this technology, MOSFET's optimized for microwave use, with 0.5-μm optically defined gate lengths and a T-gate structure, have ft values of 25 GHz (14 GHz) and fmax values of 66 GHz (41 GHz) for n-channel (p-channel) devices and have noise figure values below 1 db at 2 GHz, some of the best reported performance characteristics of any silicon-based MOSFET's to date. On-chip spiral inductors exhibit quality factors above ten. Circuit performance compares favorably with that of other CMOS-based technologies and approach performance levels similar to those obtained by silicon bipolar technologies. The results demonstrate the significant potential of this technology for microwave applications 相似文献
92.
The multicopy c subunit of the H+-transporting ATP synthase of Escherichia coli folds through the transmembrane F0 sector as a hairpin of two hydrophobic alpha-helices with the proton-translocating aspartyl-61 side chain centered in the second transmembrane helix. The number of subunits c in the F0 complex, which is thought to determine the H+-pumping/ATP stoichiometry, was previously not determined with exactness but thought to range from 9-12. The studies described here indicate that the exact number is 12. Based upon the precedent of the subunit c in vacuolar-type ATPases, which are composed of four transmembrane helices and seem to have evolved by gene duplication of an F0-type progenitor gene, we constructed genetically fused dimers and trimers of E. coli subunit c. Both the dimeric and trimeric forms proved to be functional. These results indicate that the total number of subunit c in F0 should be a multiple of 2 and 3. Based upon a previous study in which the oligomeric organization of c subunits in F0 was determined by cross-linking of Cys-substituted subunits (Jones, P. C. , Jiang, W., and Fillingame, R. H. (1998) J. Biol. Chem. 273, 17178-17185), we introduced Cys into the first and last transmembrane helices of subunit c monomers, dimers, and trimers and attempted to generate cross-linked products by oxidation with Cu(II)-(1,10-phenanthroline)2. Double Cys substitutions at two sets of positions gave rise to extensive cross-linked multimers. Multimers of the monomer that extended up to the position of c12 were correlated and calibrated with distinct cross-linked species of the appropriate doubly Cys-substituted dimers (i.e. c2, c4, . c12) and doubly Cys-substituted trimers (i.e. c3, c6, c9, c12). The results show that there are 12 copies of subunit c per F0 in E. coli, the exact number having both mechanistic and structural significance. 相似文献
93.
Responsiveness of self-reported and objective measures of disease severity in carpal tunnel syndrome
JN Katz RH Gelberman EA Wright RA Lew MH Liang 《Canadian Metallurgical Quarterly》1994,32(11):1127-1133
Responsiveness, the ability to detect meaningful clinical change, is a critical attribute of instruments used to evaluate outcomes of treatments. The authors hypothesized that self-administered symptom severity and functional status questionnaires are more responsive to clinical improvement after carpal tunnel release than traditional physical examination measures of strength and sensibility. Data were obtained from a randomized clinical trial of endoscopic versus open carpal tunnel release conducted in four university medical centers. Patients were evaluated before surgery and 3 months after surgery. Seventy-four patients indicating that they were more than 80% satisfied with the results of surgery were assumed to have clinically meaningful improvement and were the focus of the analysis. Evaluations included questionnaires assessing symptom severity, functional status, and activities of daily living as well as measurement of grip, pinch, and abductor pollicus brevis strength, and 2-point discrimination and Semmes-Weinstein pressure sensibility. Responsiveness was calculated with the standardized response mean (mean change/standard deviation of change) as well as the effect size (mean change/standard deviation of baseline values). The symptom severity scale was four times as responsive, and the functional status and activities of daily living scales were twice as responsive, as the measures of strength and sensibility. Self-administered symptom severity and functional status scales are much more responsive to clinical improvement than measures of neuromuscular impairment and should severe as primary outcomes in clinical studies of therapy for carpal tunnel syndrome. 相似文献
94.
Pigmentation phenotypes of variant extension locus alleles result from point mutations that alter MSH receptor function 总被引:2,自引:0,他引:2
LS Robbins JH Nadeau KR Johnson MA Kelly L Roselli-Rehfuss E Baack KG Mountjoy RD Cone 《Canadian Metallurgical Quarterly》1993,72(6):827-834
Coat colors in the chestnut horse, the yellow Labrador retriever, the red fox, and one type of yellow mouse are due to recessive alleles at the extension locus. Similarly, dominant alleles at this locus are often responsible for dark coat colors in mammals, such as the melanic form of the leopard, Panthera pardus. We show here that the murine extension locus encodes the melanocyte-stimulating hormone (MSH) receptor. In mice, the recessive yellow allele (e) results from a frameshift that produces a prematurely terminated, nonfunctioning receptor. The sombre (Eso and Eso-3J) and tobacco darkening (Etob) alleles, which both have dominant melanizing effects, results from point mutations that produce hyperactive MSH receptors. The Eso-3J receptor is constitutively activated, while the Etob receptor remains hormone responsive and produces a greater activation of its effector, adenylyl cyclase, than does the wild-type allele. 相似文献
95.
We report a very rare case of an avulsion of the pectoralis major tendon in association with a two-part proximal humerus fracture. Pectoralis major tendon avulsion was confirmed intraoperatively during open reduction and internal fixation of the humerus fracture. In retrospect, the preoperative radiographic finding of posterolateral and proximal displacement of the humeral shaft suggested an injury to the pectoralis major. Because others have reported that the best treatment of a pectoralis major tendon avulsion is surgical repair, we feel that it is important to suspect such an injury in a proximal humerus fracture when this anatomic displacement is present. 相似文献
96.
Johnson Robert; Hobfoll Stevan E.; Zalcberg-Linetzy Ana 《Canadian Metallurgical Quarterly》1993,6(3):266
Examined the relationships among social support knowledge, supportive behavior, intimacy with one's spouse, and satisfaction with support provided by one's spouse among 41 Israeli kibbutz couples. The hypothesis that support knowledge and support behavior influence the intimacy between couples and increase satisfaction with spouse's social support efforts was tested. Alternative causal mechanisms are explored with simultaneous equation modeling. Results indicate that satisfaction with social support behavior by one's spouse is mediated entirely by intimacy with one's spouse. Results also indicate that partner's knowledge about social support behavior directly affects intimacy and indirectly generates social support satisfaction independent of actual supportive behavior. The findings do not differ by sex. The consistency of the findings with family behavior exchange theory and implications for marital therapy are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
97.
We show for the first time that signal processing schemes based on noncoherent signal addition will require signal transfer characteristics exhibiting high degrees of curvature. We quantify this by proposing a set of single-input, dual-output, power-conserving transfer functions and generating designs based on these characteristics. We then analyze the sensitivity of such a design scheme to nonidealities in the signal level and device behavior, and show that a sampling operation is only possible for transfer characteristics with residual "low" output of less than about 10% and low intensity reflectivity higher than 98%. For single device signal loss of up to 0.1 dB, we show that the best possible crosstalk-to-noise ratio in a packet forwarder (27 dB), is limited by the availability of the sampling operation. 相似文献
98.
GQ Phan CJ Yeo JL Cameron MM Maher RH Hruban R Udelsman 《Canadian Metallurgical Quarterly》1997,122(6):989-96; discussion, 996-7
BACKGROUND: Most resectable pancreatic or peripancreatic neuroendocrine tumors are treated by enucleation or distal pancreatectomy. A minority of tumors may require pancreaticoduodenectomy for complete tumor excision because of their large size, location, or lymph node involvement. METHODS: This study reviews the management of 50 patients treated by pancreaticoduodenectomy for periampullary neuroendocrine tumors between 1962 and 1996 at a single institution. RESULTS: There were 30 men and 20 women with a mean age of 52 +/- 2 years. Functional tumors were resected in 17 patients: insulinoma, seven tumors; gastrinoma, eight tumors; vipoma, one tumor; and glucagonoma, one tumor. Tumors were classified as malignant in 29 patients and benign in 21. The median intraoperative blood loss was 800 ml, and the median number of units of blood transfused was zero. The postoperative length of stay was 20 +/- 2 days. Postoperative morbidity included 11 patients (24%) with a pancreatic fistula and four patients (8%) with a biliary fistula. There was one in-hospital death (2%), in 1967. The actuarial survival rates at 2, 5, and 7 years are 81%, 73%, and 65%, respectively. Patients with benign tumors had a significantly improved 5-year survival rate (94%) compared with those with malignant tumors (61%; p = 0.03). CONCLUSIONS: Selected patients with periampullary neuroendocrine tumors can be managed successfully by pancreaticoduodenectomy, with low mortality and acceptable morbidity rates. 相似文献
99.
RH Rau YL Chan HI Chuang CR Cheng KL Wong KH Wu TT Wei 《Canadian Metallurgical Quarterly》1997,35(2):113-118
While current psychiatric taxonomies recognise a classification of amphetamine dependence, derived from the notion of an alcohol dependence syndrome, little research has validated that such a condition exists for this drug. Current amphetamine users (N = 331), were interviewed using the World Health Organization operationalisation of DSM-III-R substance dependence criteria, and a measure of the psychological components of dependence. Structural analyses indicated that a unidimensional dependence syndrome as assessed by DSM-III-R and DSM-IV criteria exists for amphetamine, and that physiological, psychological and behavioural indicators were all important in accounting for the variance in responses. It was demonstrated that the concept of a dependence syndrome is applicable to amphetamine, and that the inclusion of the amphetamine dependence syndrome in DSM-III-R and DSM-IV is valid. 相似文献
100.
Three experiments were conducted to test fertility when sperm numbers per insemination ranged from 10 x 10(6) to 40 x 10(6) total sperm. All semen was from Holstein bulls that were on a regular schedule of semen collection. The semen was extended with heated homogenized whole milk, cooled, glycerolated, and frozen according to standard procedures. Semen was distributed to a large group of inseminators to minimize differential field effects on treatment. All experiments were a randomized block design, including a split plot in Experiment 2. In Experiment 1, data for 31,399 first inseminations distributed among treatments of 20 x 10(6), 25 x 10(6), 30 x 10(6), and 40 x 10(6) total sperm resulted in 69.8, 70.0, 70.1, and 70.1% nonreturns at 59 d, respectively. In Experiment 2, data for 18,197 first inseminations divided over treatments of 12 x 10(6), 16 x 10(6), and 20 x 10(6) total sperm resulted in 70.2, 72.4, and 70.8% nonreturns at 59 d, respectively. In Experiment 3, 38,890 first inseminations distributed over treatments of 10 x 10(6), 13 x 10(6), 16 x 10(6), and 20 x 10(6) total sperm resulted in 70.5, 72.2, 73.1, and 71.5% nonreturns at 59 d, respectively. Bull nonreturns ranged from 64 to 76% in the three trials. These results indicate that, under good conditions, total sperm numbers per straw can be reduced to 10 x 10(6) total sperm with a reduction of nonreturn rates at 59 d, for most bulls, of about 1 percentage unit from the maximum when professional inseminators are use. 相似文献