全文获取类型
收费全文 | 4222篇 |
免费 | 197篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 57篇 |
综合类 | 12篇 |
化学工业 | 708篇 |
金属工艺 | 105篇 |
机械仪表 | 81篇 |
建筑科学 | 134篇 |
矿业工程 | 5篇 |
能源动力 | 144篇 |
轻工业 | 408篇 |
水利工程 | 27篇 |
石油天然气 | 48篇 |
武器工业 | 1篇 |
无线电 | 640篇 |
一般工业技术 | 613篇 |
冶金工业 | 855篇 |
原子能技术 | 14篇 |
自动化技术 | 590篇 |
出版年
2023年 | 20篇 |
2022年 | 39篇 |
2021年 | 69篇 |
2020年 | 40篇 |
2019年 | 60篇 |
2018年 | 68篇 |
2017年 | 145篇 |
2016年 | 68篇 |
2015年 | 65篇 |
2014年 | 113篇 |
2013年 | 240篇 |
2012年 | 170篇 |
2011年 | 245篇 |
2010年 | 172篇 |
2009年 | 168篇 |
2008年 | 171篇 |
2007年 | 152篇 |
2006年 | 141篇 |
2005年 | 165篇 |
2004年 | 150篇 |
2003年 | 131篇 |
2002年 | 104篇 |
2001年 | 88篇 |
2000年 | 94篇 |
1999年 | 84篇 |
1998年 | 218篇 |
1997年 | 133篇 |
1996年 | 93篇 |
1995年 | 64篇 |
1994年 | 90篇 |
1993年 | 87篇 |
1992年 | 61篇 |
1991年 | 41篇 |
1990年 | 46篇 |
1989年 | 48篇 |
1988年 | 41篇 |
1987年 | 36篇 |
1986年 | 45篇 |
1985年 | 44篇 |
1984年 | 29篇 |
1983年 | 28篇 |
1982年 | 34篇 |
1981年 | 39篇 |
1980年 | 48篇 |
1979年 | 29篇 |
1978年 | 25篇 |
1977年 | 26篇 |
1976年 | 30篇 |
1975年 | 22篇 |
1974年 | 20篇 |
排序方式: 共有4442条查询结果,搜索用时 331 毫秒
951.
952.
红外探测器探测度D^*(T,f)探讨 总被引:1,自引:0,他引:1
本文导出了红外探测度D^*(T,f,l)与光谱匹配因数α(ωλT,rλ)之间的关系,对D^*(500K,f,l)值进行了探讨。由于实际应用中目标温度差别很大,D^*(500K,f,l)值怀实际探测结果并不一致。 相似文献
953.
954.
Void-free Au-Sn eutectic bonding of GaAs dice and its characterization using scanning acoustic microscopy 总被引:1,自引:0,他引:1
A new technique to produce perfect bonding between GaAs dice and alumina substrates is reported. Utilizing this technique,
void-free bondings have been achieved consistently. The quality of the bonded devices is confirmed by a Scanning Acoustic
Microscope (SAM) having a spatial resolution of 25 μm. Thermal cycling between -25° C and 125° C, and thermal shock between
-196° C and 135° C, have been used to assess the reliability of the specimens. The SAM was used to study the variation of
the bonds in the tests. After the tests, the bonds show no sign of degradation and the GaAs dice did not crack. Shear test
has also been performed. All the well bonded specimens passed the shear test. The shear strength correlated very well with
the SAM images of the specimens taken before the test. 相似文献
955.
I Shachar EA Elliott B Chasnoff IS Grewal RA Flavell 《Canadian Metallurgical Quarterly》1995,3(3):373-383
MHC class II molecules associate with invariant chain (li) during biosynthesis. If facilitates folding of class II molecules, interferes with their association with peptides, and is involved in their transport. The murine Ii gene encodes two chains, p31 and p41. The role of these isoforms has been studied in vitro only in inappropriate antigen-presenting cells. To circumvent this problem, we have generated invariant chain-deficient mice (delta Ii), which express exclusively the p31 and p41 isoforms. Low level expression of p31 or p41 is not sufficient for rescuing high levels of cell surface class II expression. However, low levels of the typical compact dimer conformation indicative of tight peptide binding are observed. Thus, both isoforms participate in class II folding and assembly. Furthermore, p31 and p41 retrieve the CD4+ T cell population, which is reduced in the (delta Ii) mice. Moreover, the immune response to protein antigen is restored by both isoforms. 相似文献
956.
Kuo-Qin Yan Chin Y.H. Shu-Ching Wang 《Knowledge and Data Engineering, IEEE Transactions on》1992,4(3):266-280
Traditionally, the problems of Byzantine agreement, consensus, and interactive consistency are studied in a fully connected network with processors in malicious failure only. Such problems are reexamined with the assumption of malicious faults on both processors and links. The proposed protocols use the minimum number of message exchanges and can tolerate the maximum number of allowable faulty components to make each fault-free processor reach a common agreement for the cases of processor failure, link failure, or processor and link failure 相似文献
957.
KH Oh C Ahn JH Park JE Oh HJ Chin JS Han S Kim JG Chi MH Park JS Lee 《Canadian Metallurgical Quarterly》1997,12(2):232-237
We present a 30-year-old male patient who was initially diagnosed as minimal change nephrotic syndrome, 5 years later, the patient developed a localized form of idiopathic retroperitoneal fibrosis (IRF). An elevated ESR and concomitant nephrotic syndrome in the patient suggested the immunologic nature of IRF, IRF has been reported in association with collagen diseases and rarely with proliferative and nonproliferative glomerulopathies. To our knowledge, the association between minimal change lesion (MC) and IRF has not been reported. Furthermore, the fact that IRF presented itself as an abdominal mass and lacked systemic symptoms was also unusual. 相似文献
958.
Comparative study of stochastic algorithms for system optimizationbased on gradient approximations 总被引:2,自引:0,他引:2
Chin D.C. 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》1997,27(2):244-249
Stochastic approximation (SA) algorithms can be used in system optimization problems for which only noisy measurements of the system are available and the gradient of the loss function is not. This type of problem can be found in adaptive control, neural network training, experimental design, stochastic optimization, and many other areas. This paper studies three types of SA algorithms in a multivariate Kiefer-Wolfowitz setting, which uses only noisy measurements of the loss function (i.e., no loss function gradient measurements). The algorithms considered are: the standard finite-difference SA (FDSA) and two accelerated algorithms, the random directions SA (RDSA) and the simultaneous-perturbation SA (SPSA). RDSA and SPSA use randomized gradient approximations based on (generally) far fewer function measurements than FDSA in each Iteration. This paper describes the asymptotic error distribution for a class of RDSA algorithms, and compares the RDSA, SPSA, and FDSA algorithms theoretically (using mean-square errors computed from asymptotic distributions) and numerically. Based on the theoretical and numerical results, SPSA is the preferable algorithm to use. 相似文献
959.
960.
QT dispersion and risk factors for sudden cardiac death in patients with hypertrophic cardiomyopathy
G Yi P Elliott WJ McKenna K Prasad S Sharma XH Guo AJ Camm M Malik 《Canadian Metallurgical Quarterly》1998,82(12):1514-1519
Growth hormone (GH) treatment is associated with a reduction in fat mass in healthy and GH-deficient (GHD) subjects. This is mainly mediated via a direct GH action on adipose cells and stimulation of lipolysis. Leptin is secreted from adipose tissue and may be involved in signaling information about adipose tissue stores to the brain. Hormonal regulation of leptin is still not fully elucidated, and in the present study, we investigated both the long-term (4-month) and short-term (28-hour) GH effects on serum leptin and leptin gene expression in subcutaneous adipose tissue. In GHD adults (n = 24), leptin correlated with most estimates of adiposity (r = .62 to .86), as previously found in healthy subjects. However, no correlation was observed with intraabdominal fat determined by computed tomographic (CT) scan (INTRA-CT). GH treatment for 4 months had no independent effect on either serum leptin or leptin gene expression. In a short-term study, we found that fasting gradually reduced leptin levels in both healthy men and GHD adults, with a maximum reduction of 58% to 60% (P < .01) after 31 hours. No independent effect of GH suppression or GH substitution on serum leptin was found during fasting. Adipose tissue leptin mRNA correlated with serum leptin (r = .51, P < .01) and the body mass index ([BMI] r = .55, P < .05). Serum leptin levels and gene expression were significantly higher in women compared with men (26.6 +/- 5.8 v 10.0 +/- 1.30 ng/mL, P < .05). However, in regression analysis accounting for the gender differences in subcutaneous femoral adipose tissue (FEM-CT), the difference in serum leptin disappeared, indicating that subcutaneous femoral fat or factors closely related to femoral fat (eg, sex hormones) may be causal factors for the gender difference in leptin. 相似文献