全文获取类型
收费全文 | 12226篇 |
免费 | 699篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 141篇 |
综合类 | 16篇 |
化学工业 | 3018篇 |
金属工艺 | 161篇 |
机械仪表 | 273篇 |
建筑科学 | 444篇 |
矿业工程 | 25篇 |
能源动力 | 387篇 |
轻工业 | 1803篇 |
水利工程 | 67篇 |
石油天然气 | 44篇 |
无线电 | 822篇 |
一般工业技术 | 1964篇 |
冶金工业 | 1628篇 |
原子能技术 | 79篇 |
自动化技术 | 2071篇 |
出版年
2023年 | 110篇 |
2022年 | 345篇 |
2021年 | 412篇 |
2020年 | 287篇 |
2019年 | 284篇 |
2018年 | 413篇 |
2017年 | 437篇 |
2016年 | 481篇 |
2015年 | 348篇 |
2014年 | 503篇 |
2013年 | 930篇 |
2012年 | 771篇 |
2011年 | 857篇 |
2010年 | 661篇 |
2009年 | 620篇 |
2008年 | 661篇 |
2007年 | 538篇 |
2006年 | 438篇 |
2005年 | 350篇 |
2004年 | 286篇 |
2003年 | 260篇 |
2002年 | 261篇 |
2001年 | 163篇 |
2000年 | 155篇 |
1999年 | 150篇 |
1998年 | 549篇 |
1997年 | 311篇 |
1996年 | 215篇 |
1995年 | 147篇 |
1994年 | 118篇 |
1993年 | 121篇 |
1992年 | 44篇 |
1991年 | 48篇 |
1990年 | 35篇 |
1989年 | 49篇 |
1988年 | 39篇 |
1987年 | 33篇 |
1986年 | 31篇 |
1985年 | 47篇 |
1984年 | 37篇 |
1983年 | 26篇 |
1982年 | 46篇 |
1981年 | 42篇 |
1980年 | 29篇 |
1979年 | 24篇 |
1978年 | 29篇 |
1977年 | 51篇 |
1976年 | 42篇 |
1975年 | 21篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
TG Orsière MM Chauvet MH Dell''Amico MJ Bourdeaux 《Canadian Metallurgical Quarterly》1995,291(3):237-243
Hepatocyte growth factor (HGF) is a potent mitogen for the maturation of hepatocytes in vitro which plays a role in liver regeneration in vivo. In addition, transforming growth factor-beta 1 (TGF-beta 1) is also a potent regulator of liver regeneration. In attempting to clarify the mechanisms related to liver regeneration after partial hepatectomy, we investigated the expression of HGF and TGF-beta 1 in rats with liver cirrhosis (LC). A rat model of LC was prepared using carbon tetrachloride (CCl4). The expression of HGF mRNA in both the LC and control groups showed a similar time-course with the highest expression seen at 18h after a 70% hepatectomy. The expression of TGF-beta 1 mRNA peaked at 18h after partial hepatectomy in the LC group and at 48h in the control group. The 5-bromo-2'-deoxyuridine (BrdU) labeling index for the LC group at 24, 48, and 72 h after partial hepatectomy was 9.2%, 5.9%, and 1.8%, while for the control group it was 7.0%, 11.7%, and 6.8%, respectively. The BrdU labeling index in the LC group was thus suppressed earlier than that in the control group. We therefore postulate that regeneration of the remnant liver in the presence of LC accelerates immediately after partial hepatectomy, but the extent of regeneration is insufficient because of an early cessation due to an early expression of TGF-beta 1. 相似文献
22.
Wistar rats, eight days old, were subjected to permanent bilateral forebrain ischemia, followed by hypoxia for 15 minutes. A cerebral infarct, mainly involving the cerebral neocortex, hippocampus, amygdala, striatum and subcortical white matter was produced. Neurons and glia showing punctate chromatin condensation and karyorrhectic cells were observed 12 hours after hypoxia-ischemia. Their number increased during the first two days and recruitment of cells with degenerating nuclei occurred until day five. In situ labeling of nuclear DNA fragmentation stained many normal-appearing nuclei, as well as punctate chromatin condensations and nuclear fragments in karyorrhectic cells. Delayed neuronal death in the CA1 area of the hippocampus was observed after 20 minutes of transient forebrain ischemia in the adult gerbil. In situ labeling of nuclear DNA fragmentation demonstrated stained punctate chromatin condensation in a few degenerating cells at 48 hours post-ischemia. Substantial labeling of CA1 neurons occurred in the fourth day. Agarose gel electrophoresis of extracted brain DNA from ischemic infant rats and adult gerbils showed a ladder-type pattern which is typical of nuclear DNA fragmentation into oligonucleosomal fragments (internucleosomal cleavage). These findings suggest that endonuclease(s) activation may play a role in cell death induced by different forms of hypoxia-ischemia. 相似文献
23.
F Gaymard G Pilot B Lacombe D Bouchez D Bruneau J Boucherez N Michaux-Ferrière JB Thibaud H Sentenac 《Canadian Metallurgical Quarterly》1998,94(5):647-655
SKOR, a K+ channel identified in Arabidopsis, displays the typical hydrophobic core of the Shaker channel superfamily, a cyclic nucleotide-binding domain, and an ankyrin domain. Expression in Xenopus oocytes identified SKOR as the first member of the Shaker family in plants to be endowed with outwardly rectifying properties. SKOR expression is localized in root stelar tissues. A knockout mutant shows both lower shoot K+ content and lower xylem sap K+ concentration, indicating that SKOR is involved in K+ release into the xylem sap toward the shoots. SKOR expression is strongly inhibited by the stress phytohormone abscisic acid, supporting the hypothesis that control of K+ translocation toward the shoots is part of the plant response to water stress. 相似文献
24.
25.
B Amy de la Bretèque 《Canadian Metallurgical Quarterly》1995,116(4):271-272
The adolescent's breaking of the voice is the result of the substitution of the chest voice (or heavy mechanism) for the head voice (or light mechanism). In cases of late breaking, the voice is abnormally high-pitched and feeble, often with a distorted timbre, while the larynx is normal and pubescent. Such people are generally not fully aware of their voices' real nature. Therapy classically resorts to laryngeal manipulations, of which a new technique is put forward. Another therapeutic approach is based, on the one hand, on critical listening compared with a control male voice, thus enabling the subject to become aware of his own voice, and, on the other hand, on high intensity work which helps passing from head to chest voice. 相似文献
26.
Wrinkling is a well known phenomenon experimented by tension membranes in Civil Engineering applications. This paper will
present an efficient numerical technique for the computational simulation of such wrinkles in a prestressed membrane. In particular,
the relaxed energy approach (Pipkin in IMA J Appl Math 36:85–99, 1986) is particularized for prestressed membranes (Gil in
Textile composites and inflatable structures, CIMNE, 2003) undergoing moderate strains. Wrinkling conditions in terms of the
Euler-Lagrange finite deformation tensor along principal directions will be obtained. This will provide a framework to describe
properly the initial instant when wrinkles start to be encountered in a prestressed Saint Venant–Kirchhoff hyperelastic membrane.
Subsequently, a modified Helmholtz’s free energy functional will be introduced with the purpose of describing the modified
constitutive behaviour of the continuum after the onset of wrinkling. Consistent derivations of the stress tensor as well
as the constitutive tensor will de depicted. The results will be particularized for membranes and cables in a Finite Element
discretization basis. Some numerical examples will prove the accuracy and robustness of the described algorithm. 相似文献
27.
M. Lamirand J. -L. Bonnentien S. Guérin G. Ferrière J. -P. Chevalier 《Metallurgical and Materials Transactions A》2006,37(8):2369-2378
The effect of added oxygen in the range of 1000 to 4000 wt ppm on the microstructures of a Ti-48Al-2Cr-2Nb alloy has been
investigated and compared to the microstructures for a high-purity alloy. For specimens cooled from theα phase, interstitial oxygen stabilizes the lamellar microstructure with respect toγ grains, with higher than equilibrium values for theα
2 volume fraction. For specimens cooled from theα +γ phase field, the lamellar microstructure still tends to be favored by oxygen, but it is found that the phase volume fractions
are not significantly different from equilibrium values. This suggests that interstitial O essentially reduces the kinetics
of theα toα +γ transformation. Thus, interstitial oxygen will have a strong effect on microstructures obtained by continuous cooling fromα, but significantly less on those, such as the duplex microstructure, obtained by long treatment in theα +γ phase field. In general, increased O content is well correlated with reduced ductility. Finally, the role of interstitial
oxygen on this phase transformation is discussed. 相似文献
28.
In this paper we develop and compare several heuristic methods for solving the general two-dimensional cutting stock problem.
We follow the Gilmore-Gomory column generation scheme in which at each iteration a new cutting pattern is obtained as the
solution of a subproblem on one stock sheet. For solving this subproblem, in addition to classical dynamic programming, we
have developed three heuristic procedures of increasing complexity, based on GRASP and Tabu Search techniques, producing solutions
differing in quality and in time requirements. In order to obtain integer solutions from the fractional solutions of the Gilmore-Gomory
process, we compare three rounding procedures, rounding up, truncated branch and bound and the solution of a residual problem.
We have coded and tested all the combinations of algorithms and rounding procedures. The computational results obtained on
a set of randomly generated test problems show their relative efficiency and allow the potential user to choose from among
them, according to the available computing time.
Rceived: January 9, 2001 / Accepted: December 10, 2001 相似文献
29.
This paper informs about an evaluation of Spanish educational research journals using the modality of reputation inferred
from survey data. Univariate and multivariate patterns are offered. Specifically cluster analysis and non-parametric multidimensional
scaling reveal themselves as useful methods to inquire the complexity of this scientometric question which is the evaluation
of periodical series.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
30.
B Quinting JM Reyrat D Monnaie G Amicosante V Pelicic B Gicquel JM Frère M Galleni 《Canadian Metallurgical Quarterly》1997,406(3):275-278
Changes in motor function were assessed in male rats after injecting graded doses (100, 200, 400, and 800 mg/kg, IP) of ammonium chloride and ammonium acetate. The effects were correlated with the concentrations of ammonia and glucose in the brain and blood. Spontaneous motor activity and motor coordination were inhibited after injecting 100 and 200 mg/kg, whereas with 400 and 800 mg/kg the animals exhibited convulsive movements. A dose-dependent increase was found in the concentrations of ammonia and glucose in both blood and brain. These were restored, 25 min after treatment, to control levels in the blood and not in the brain. A correlation was found between the time courses of inhibitory motor events and a rise in brain ammonia levels. Convulsant action of ammonium salts was accompanied by a marked elevation of ammonia and glucose concentration in the brain. The findings suggest that detoxication of diffused ammonia is a rate-limiting process in the brain and that ammonia, at toxic concentrations, decreases glucose utilization in the brain, resulting in an inhibition of motor function. A very high concentration of ammonia in the brain, although inhibiting glucose utilization, produces clonic convulsions probably by activating directly the motor neurons. 相似文献