全文获取类型
收费全文 | 22305篇 |
免费 | 893篇 |
国内免费 | 312篇 |
专业分类
电工技术 | 463篇 |
综合类 | 543篇 |
化学工业 | 3625篇 |
金属工艺 | 516篇 |
机械仪表 | 727篇 |
建筑科学 | 846篇 |
矿业工程 | 178篇 |
能源动力 | 559篇 |
轻工业 | 2072篇 |
水利工程 | 242篇 |
石油天然气 | 177篇 |
武器工业 | 27篇 |
无线电 | 2365篇 |
一般工业技术 | 2773篇 |
冶金工业 | 5414篇 |
原子能技术 | 168篇 |
自动化技术 | 2815篇 |
出版年
2023年 | 91篇 |
2022年 | 262篇 |
2021年 | 460篇 |
2020年 | 263篇 |
2019年 | 329篇 |
2018年 | 379篇 |
2017年 | 357篇 |
2016年 | 397篇 |
2015年 | 347篇 |
2014年 | 523篇 |
2013年 | 1013篇 |
2012年 | 789篇 |
2011年 | 967篇 |
2010年 | 743篇 |
2009年 | 810篇 |
2008年 | 795篇 |
2007年 | 814篇 |
2006年 | 703篇 |
2005年 | 603篇 |
2004年 | 681篇 |
2003年 | 899篇 |
2002年 | 1185篇 |
2001年 | 1013篇 |
2000年 | 589篇 |
1999年 | 604篇 |
1998年 | 1929篇 |
1997年 | 1195篇 |
1996年 | 827篇 |
1995年 | 540篇 |
1994年 | 387篇 |
1993年 | 468篇 |
1992年 | 203篇 |
1991年 | 162篇 |
1990年 | 158篇 |
1989年 | 150篇 |
1988年 | 141篇 |
1987年 | 120篇 |
1986年 | 121篇 |
1985年 | 156篇 |
1984年 | 85篇 |
1983年 | 94篇 |
1982年 | 89篇 |
1981年 | 112篇 |
1980年 | 114篇 |
1979年 | 61篇 |
1978年 | 52篇 |
1977年 | 127篇 |
1976年 | 265篇 |
1975年 | 54篇 |
1973年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
91.
BW Woodward JW Mabry MT See JK Bertrand LL Benyshek 《Canadian Metallurgical Quarterly》1993,71(8):2040-2046
An animal model and computer software were developed to conduct across-herd genetic evaluations using data from producers participating in the Sow Productivity Index program of the American Yorkshire Club. The final data set consisted of 61,596 litter records from 1986 to early 1990. The animal model included fixed contemporary group effects and random additive direct, service sire, permanent environmental, and residual effects. Additive genetic relationships among animals were included. A separate relationship matrix for service sires and their sires was also included. A data set similar to the Yorkshire field data was simulated to use in testing the animal model. The simulated data set consisted of 40 herds, each with 120 reproducing dams and either four or five sires. Six generations of simulated data were produced, resulting in 20,605 litter records. These records were then evaluated using the animal model for number of pigs born alive. Finally, correlations between the true breeding values from the simulation and the predicted breeding values were computed. The correlation between the 918 true and predicted sire breeding values was considerably lower for the animal model without a service sire effect than when it was included (.53 vs .74, respectively). However, the difference was cut in half (.66 vs .77) when only sires with greater than five daughter records were included. The high accuracy of the animal model with a random service sire effect indicates that the proposed model adequately accounts for the variation found in records for number of pigs born alive. 相似文献
92.
V Robert F De Giorgi ML Massimino M Cantini T Pozzan 《Canadian Metallurgical Quarterly》1998,273(46):30372-30378
Direct monitoring of the free Ca2+ concentration in the sarcoplasmic reticulum (SR) was carried out in rat skeletal myotubes transfected with a specifically targeted aequorin chimera (srAEQ). Myotubes were also transfected with a chimeric aequorin (erAEQ) that we have demonstrated previously is retained in the endoplasmic reticulum (ER). Immunolocalization analysis showed that although both recombinant proteins are distributed in an endomembrane network identifiable with immature SR, the erAEQ protein was retained also in the perinuclear membrane. The difficulty of measuring [Ca2+] in 100-1000 microM range was overcome with the use of the synthetic coelenterazine analogue, coelenterazine n. We demonstrate that the steady state levels of [Ca2+] measured with srAEQ is around 300 microM, whereas that measured with erAEQ is significantly lower, i.e. around 200 microM. The effects of caffeine, high KCl, and nicotinic receptor stimulation, in the presence or absence of external calcium or after blockade of the Ca-ATPase, were investigated with both chimeras. The kinetics of [Ca2+] changes revealed by the erAEQ were similar, but not identical, neither quantitatively nor qualitatively, to those monitored with the srAEQ, indicating that at this stage of muscle development, differences exist between SR and ER in their mechanisms of Ca2+ handling. The functional implications of these findings are discussed. 相似文献
93.
The a.c. conductivity of the proteins lysozyme and subtilisin, both in their active and inactive or inhibited forms were determined theoretically. For this, quantum mechanical calculations and a random walk theory were used. The conclusions are that these enzymatic proteins can easily transport electrons which is most probably important in their role as catalysators of biochemical reactions. The electron transport is sensitive to three-dimensional changes of the active sites of these enzymes which have more flexibility than the whole molecule. Therefore, the flexibility of the active sites of enzyme catalysts is not only important for the conformational fitting with the reactants, but also strongly influences the transport in biochemical reactions. 相似文献
94.
Time dispersion (TD) is computed for large neutron detectors using plastic scintillators. It is shown that TD seen by the photomultiplier (PM) tube does not necessarily increase with incident neutron energy, which is a result not fully in agreement with the usual finding 相似文献
95.
96.
A method for reconstitution of membrane proteins into unilamellar liposomes is described. The model enzyme was the F0F1 ATP synthase from mitochondria when in complex or free from its inhibitor protein. The enzymes were first solubilized with either of two detergents, i.e., n-dodecyl-beta-D maltoside or lauryldimethylamine oxide. After solubilization, the enzymes were passed through a column of Sepharose-AH using an ADP/sodium cholate selective elution buffer. The enzymes recovered from the column were subsequently passed through a centrifuge column of Sephadex G-50 fine. The eluate contained liposomes in which the F0F1 complex (with and without inhibitor protein) had been reconstituted. The reconstituted enzymes were capable of hydrolyzing ATP with formation of electrochemical H+ gradients. They also catalyzed the ATP-Pi exchange reactions. Thus the F0F1 complex which is formed by 18 subunits can be rapidly reconstituted into liposomes in a fully functional state. Moreover the data show that the interactions between the enzyme and its inhibitor protein are not perturbed in the reconstitution procedure. 相似文献
97.
JF Delaloye S Leyvraz E Outcha Adjahoto J Bauer P De Grandi 《Canadian Metallurgical Quarterly》1996,19(2):204-206
We report two cases of metastatic non-functioning pancreatic endocrine tumour with very elevated plasma levels of alpha-fetoprotein. In these two cases, serial plasma levels of alpha-fetoprotein, initially normal, correlated well with hepatic tumour progression and were associated with fatal outcome. These results suggest that elevated plasma concentration of alpha-fetoprotein may be caused by metastatic pancreatic endocrine tumour and than alpha-fetoprotein serial measurement may be useful in prognostic evaluation. 相似文献
98.
A. Ureña J. M. Gomez De Salazar J. Quiñones S. Merino J. Martin 《Journal of Materials Science》1996,31(3):807-817
Diffusion bonds have been produced between sheets of an Al-Li-Cu-Mg-Zr alloy using aluminium-4% copper vapour deposited metallic interlayers. Microstructural changes occurred both in the parent alloy and in the bond interface after diffusion bonding cycles and post-bonding heat treatments were analysed. Different metallographic techniques (light microscopy, scanning and transmission electron microscopy) have been used. Diffusion bonding trials were carried out using the same alloy (AA8090), both in non-superplastic (T6) and superplastic conditions. Differences in their behaviours in relation to diffusion bonding were observed. 相似文献
99.
100.
This paper concerns the plasticity constitutive laws in small strain. In the thermodynamic approach developed here, the key concept is that of internal variables. The differential nature of plasticity law has been pointed out for a long time. If we unite the invariance condition of these laws in a state variable transformation, this involves, ultimately, that the natural mathematic frame of plasticity theory is Differential Geometry. The system state is defined as a point of a differentiable manifold. The state variable are the local coordinates of this point in a chart. The internal stresses are the components of a covariant vector of the cotangent bundle to internal state manifold and the elastic domain is a convex part of cotangent vector space. The plastic yield criteria such as von Mises condition define a Riemannian structure over the manifold. The metric element is identified with the internal dissipation element. Constitutive laws link the covariant derivatives of the thermodynamic stress with the state variable. Hardening modulus splits up in two parts, kinematic hardening and metric hardening. This last is defined by Christoffel connection coefficients. Applied to von Mises isotropic yield condition, the metric hardening is identified with isotropic hardening. The Baltov-Sawczuk model is also analysed. The use of appropriate polar coordinates simplifies significantly the computations. Generalization to a significant category of non-differentiable yield criteria, such as Tresca condition, is considered by introducting a metric tensor family. The adaptation of Drucker's postulate to the proposed model requires the introduction of parallel transport of the internal stress covector. Generally, this transport is different over distinctive paths joining two points. This fact expresses internal state manifold curvature. The Riemann-Christoffel tensor is computed for von Mises, Baltov-Sawczuk and Tresca models. 相似文献