全文获取类型
收费全文 | 4818篇 |
免费 | 0篇 |
专业分类
化学工业 | 16篇 |
金属工艺 | 2篇 |
建筑科学 | 1篇 |
矿业工程 | 1篇 |
能源动力 | 2篇 |
轻工业 | 2篇 |
水利工程 | 2篇 |
无线电 | 2篇 |
一般工业技术 | 15篇 |
冶金工业 | 4765篇 |
自动化技术 | 10篇 |
出版年
2023年 | 1篇 |
2020年 | 1篇 |
2014年 | 1篇 |
2013年 | 4篇 |
2012年 | 1篇 |
2011年 | 2篇 |
2010年 | 1篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 1篇 |
2006年 | 1篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2002年 | 1篇 |
2001年 | 3篇 |
1999年 | 152篇 |
1998年 | 1479篇 |
1997年 | 857篇 |
1996年 | 556篇 |
1995年 | 322篇 |
1994年 | 251篇 |
1993年 | 300篇 |
1992年 | 44篇 |
1991年 | 63篇 |
1990年 | 60篇 |
1989年 | 72篇 |
1988年 | 61篇 |
1987年 | 68篇 |
1986年 | 55篇 |
1985年 | 65篇 |
1984年 | 3篇 |
1983年 | 9篇 |
1982年 | 17篇 |
1981年 | 18篇 |
1980年 | 38篇 |
1979年 | 1篇 |
1978年 | 7篇 |
1977年 | 90篇 |
1976年 | 187篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有4818条查询结果,搜索用时 15 毫秒
101.
Extracellular amyloid beta-peptide (A beta) deposition is a pathological feature of Alzheimer's disease and the aging brain. Intracellular A beta accumulation is observed in the human muscle disease, inclusion body myositis. A beta has been reported to be toxic to neurons through disruption of normal calcium homeostasis. The pathogenic role of A beta in inclusion body myositis is not as clear. Elevation of intracellular calcium following application of calcium ionophore increases the generation of A beta from its precursor protein (betaAPP). A receptor-based mechanism for the increase in A beta production has not been reported to our knowledge. Here, we use caffeine to stimulate ryanodine receptor (RYR)-regulated intracellular calcium release channels and show that internal calcium stores also participate in the genesis of A beta. In cultured HEK293 cells transfected with betaAPP cDNA, caffeine (5-10 mM) significantly increased the release of A beta fourfold compared with control. These actions of caffeine were saturable, modulated by ryanodine, and inhibited by the RYR antagonists ruthenium red and procaine. The calcium reuptake inhibitors thapsigargin and cyclopiazonic acid potentiated caffeine-stimulated A beta release. NH4Cl and monensin, agents that alter acidic gradients in intracellular vesicles, abolished both the caffeine and ionophore effects. Immunocytochemical studies showed some correspondence between the distribution patterns of RYR and cellular betaAPP immunoreactivities. The relevance of these findings to Alzheimer's disease and inclusion body myositis is discussed. 相似文献
102.
103.
P Kaminopetros E Jauniaux P Kane M Weston KH Nicolaides DJ Campbell 《Canadian Metallurgical Quarterly》1997,70(835):750-753
An unusual case of fetal lymphangioma diagnosed before delivery is reported in a second trimester pregnant woman. The lymphangioma was suspected at 28 weeks on the basis of the ultrasound appearances and progression of the lesions with advancing gestation. MRI was used to evaluate the extent and the tissue characteristics of the lesions. Cytology of the fluid aspirated from the cystic lesions showed abundant lymphocytes and macrophages, confirming the diagnosis of a lymphangioma. The parents opted for a pregnancy termination because of the rapid growth of the lesions and the poor prognosis. It is suggested that the combination of these tests could enable the early diagnosis of these tumours at a stage when the lesion is relatively limited and accessible to therapy in utero. 相似文献
104.
105.
In this retrospective cephalometric study of mandibular rotational change, we studied 60 cases. All patients were treated with full fixed appliances and exhibited an opening rotation of at least 1.5 degrees during treatment, as measured on the basis of the angle of the Y-axis to the sella-nasion line (SN). Our objective was to determine whether this opening rotation was sustained during retention. Paired t tests were used to test the hypothesis that the treatment change or opening rotation was stable and that these patients did not return to their original mandible-to-cranium relationship in the posttreatment period. Stepwise regression analysis was used to determine which (if any) changes in the independent variables during treatment could predict the subsequent behavior of the angle of the mandibular plane to the SN and the angle of the Y-axis to the SN during retention. During treatment, the mean increase in the angle of the Y-axis to the SN was 2.43 degrees. After an average posttreatment period of 54 months, this angle was reduced on average by only 0.73 degrees. Stepwise linear-regression analysis indicated that none of the treatment changes seen in the independent variables strongly predicted the ensuing closing rotation seen during retention. The correlation coefficient between the Y-axis angle and the mandibular-plane angle during treatment was 0.67. Mandibular opening rotations as a consequence of orthodontic treatment do not invariably return to the pretreatment value, and their negative effects--although sometimes small--cannot be discounted. Because the preponderant evidence of a closing rotation occurs in the terminal pubertal growth stages, the net effect may be even more significant. 相似文献
106.
A George J Gui NA Jenkins DJ Gilbert NG Copeland A Veis 《Canadian Metallurgical Quarterly》1994,42(12):1527-1531
Dentinogenesis is being used as a model for understanding the biomineralization process. The odontoblasts synthesize a structural matrix comprised of Type I collagen fibrils which define the basic architecture of the tissue. The odontoblasts also synthesize and deliver a number of dentin-specific acidic macromolecules into the extracellular compartment. These acidic macromolecules may be involved in regulating the ordered deposition of hydroxyapatite crystals within the matrix. AG1 is the first tooth-specific acidic macromolecule to have been cloned and sequenced. To identify which cells of the rat incisor pulp/odontoblast complex were responsible for synthesis of AG1, in situ hybridization was used. Digoxigenin labeled sense and anti-sense AG1 riboprobes were prepared. The AG1 mRNA was found to be expressed in the mature secretory odontoblasts. Neither pulp cells nor pre-odontoblasts showed any staining with the anti-sense probes. Chromosomal localization studies placed the AG1 gene on mouse chromosome 5q21, in tight linkage with Fgf5. AG1 has been renamed Dmp1 (dentin matrix protein 1) in accordance with present chromosomal nomenclature. Mouse 5q21 corresponds to the 4q21 locus in humans. This is the locus for the human tooth mineralization disorder dentinogenesis imperfecta Type II (DI-II). These data suggest that the Dmp1 gene is involved in mineralization and is a candidate gene for DI-II. 相似文献
107.
Back pain is an important public health problem but there is a paucity of knowledge about risk factors and causal mechanisms. Previous studies have shown that tall men are more at risk of back pain, although observations in women have been less consistent. This paper presents findings from a national longitudinal study of 3262 men and women aged 43 yr. Standing height and sitting height were related to 18-month reported prevalence of 'sciatica, lumbago or severe backache' in both men and women. The paper investigates explanations for these findings using previously collected data on childhood growth and detailed lifetime occupational histories. Neither greater susceptibility of tall men to heavy lifting, nor the timing of growth, were able to account for these relationships. To assess further the association between height and back pain, information is needed on the relationship between stature and characteristics of spinal structure. 相似文献
108.
BACKGROUND: Desflurane (difluoromethyl 1-fluoro 2,2,2-trifluoroethyl ether) is a new inhalational anesthetic currently under investigation for use in humans. Recently, the authors showed that desflurane is a trigger of malignant hyperthermia (MH) in susceptible swine. To date, there has been no in vivo comparison of the relative ability of inhalational anesthetics to trigger MH. The effects of desflurane, isoflurane, and halothane on six MH-susceptible purebred and six MH-susceptible mixed-bred Pietrain swine were examined. METHODS: The animals were exposed to 1 MAC and 2 MAC (if MH was not triggered after 1 MAC hour) doses of each of the three volatile anesthetics in random sequence at 7-10-day intervals and changes in end-tidal CO2, arterial blood gases, serum lactate, core and muscle temperature, blood pressure, and heart rate were measured. RESULTS: There was a statistical difference between anesthetics in the time required to trigger MH; halothane exposure resulted in the fastest onset of an MH episode (20 +/- 5 min), compared with isoflurane (48 +/- 24 min) and desflurane (65 +/- 28 min), both of which required significantly longer exposures. There was no statistical difference between the MH purebred and mixed-bred swine in the time required to trigger MH (defined as a PaCO2 of 70 mmHg) with a given agent, and time to triggering was also independent of the order of exposure to the three anesthetics. Malignant hyperthermia susceptibility was confirmed in ten surviving animals, by both in vivo succinylcholine challenge and in vitro contracture testing. CONCLUSIONS: Although all three volatile anesthetics triggered MH, exposure to halothane resulted in significantly shorter times to MH triggering when compared with desflurane and isoflurane. 相似文献
109.
JF McCarthy DJ Cook MG Massad Y Sano KJ O''Malley NR Ratliff RW Stewart NG Smedira RC Starling JB Young PM McCarthy 《Canadian Metallurgical Quarterly》1998,14(2):197-200
28 isolates of canine parvovirus type-2 (CPV-2) were obtained from dogs with hemorrhagic gastroenteritis in Italy. The antigenic structure of CPV-2 isolates was characterized, using four discriminating monoclonal antibodies. In addition, four vaccinal strains were examined. Similar to reports from Australia and the United Kingdom, a much higher prevalence of CPV-2a (25/28 isolates) was observed than the other variant type, CPV-2b (3/28 isolates). DNA fragments (2.2 kbp) of representative strains of CPV-2, CPV-2a and CPV-2b were amplified by the polymerase chain reaction (PCR) and the products were digested by the restriction enzymes (RE) RsaI, HpaII, HindIII and PvuII. The RvaI enzyme allows the differentiation of CPV-2 from CPV-2a and CPV-2b. 相似文献
110.
The region of the genome encoding the glucose-6-phosphate dehydrogenase gene zwf was analysed in a unicellular cyanobacterium, Synechococcus sp. PCC 7942, and a filamentous, heterocystous cyanobacterium, Anabaena sp. PCC 7120. Comparison of cyanobacterial zwf sequences revealed the presence of two absolutely conserved cysteine residues which may be implicated in the light/dark control of enzyme activity. The presence in both strains of a gene fbp, encoding fructose-1,6-bisphosphatase, upstream from zwf strongly suggests that the oxidative pentose phosphate pathway in these organisms may function to completely oxidize glucose 6-phosphate to CO2. The amino acid sequence of fructose-1,6-bisphosphatase does not support the idea of its light activation by a thiol/disulfide exchange mechanism. In the case of Anabaena sp. PCC 7120, the tal gene, encoding transaldolase, lies between zwf and fbp. 相似文献