全文获取类型
收费全文 | 18985篇 |
免费 | 678篇 |
国内免费 | 44篇 |
专业分类
电工技术 | 237篇 |
综合类 | 24篇 |
化学工业 | 3739篇 |
金属工艺 | 468篇 |
机械仪表 | 397篇 |
建筑科学 | 948篇 |
矿业工程 | 108篇 |
能源动力 | 600篇 |
轻工业 | 1634篇 |
水利工程 | 175篇 |
石油天然气 | 68篇 |
无线电 | 1457篇 |
一般工业技术 | 3365篇 |
冶金工业 | 3425篇 |
原子能技术 | 116篇 |
自动化技术 | 2946篇 |
出版年
2023年 | 123篇 |
2022年 | 210篇 |
2021年 | 331篇 |
2020年 | 234篇 |
2019年 | 271篇 |
2018年 | 368篇 |
2017年 | 378篇 |
2016年 | 413篇 |
2015年 | 339篇 |
2014年 | 514篇 |
2013年 | 1219篇 |
2012年 | 825篇 |
2011年 | 1166篇 |
2010年 | 800篇 |
2009年 | 829篇 |
2008年 | 931篇 |
2007年 | 872篇 |
2006年 | 759篇 |
2005年 | 743篇 |
2004年 | 594篇 |
2003年 | 542篇 |
2002年 | 526篇 |
2001年 | 332篇 |
2000年 | 303篇 |
1999年 | 328篇 |
1998年 | 355篇 |
1997年 | 298篇 |
1996年 | 326篇 |
1995年 | 303篇 |
1994年 | 290篇 |
1993年 | 262篇 |
1992年 | 259篇 |
1991年 | 161篇 |
1990年 | 230篇 |
1989年 | 203篇 |
1988年 | 167篇 |
1987年 | 166篇 |
1986年 | 156篇 |
1985年 | 187篇 |
1984年 | 197篇 |
1983年 | 162篇 |
1982年 | 170篇 |
1981年 | 168篇 |
1980年 | 143篇 |
1979年 | 165篇 |
1978年 | 123篇 |
1977年 | 121篇 |
1976年 | 162篇 |
1975年 | 125篇 |
1973年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
S Tetali E Abrams S Bakshi M Paul N Oyaizu S Pahwa 《Canadian Metallurgical Quarterly》1996,12(8):669-675
The relationship of virus load to clinical disease progression in HIV-infected children remains to be elucidated. In this study, HIV-1 proviral DNA load was determined in peripheral blood mononuclear cells (PBMCs) by the quantitative competitive DNA polymerase chain reaction assay (QC-PCR) in 47 HIV-infected children subdivided by age (group I, < or = 2 years; group II, > or = 5 years), who were further categorized to include 12 rapid progressors (RP, age < or = 2 years, Centers for Disease Control [CDC] defined clinical category C and/or immune category 3, or death before age 2 years) and slow progressors (SP, age > or = 5 years, excluding CDC categories C and/or immune category 3). Significantly higher mean proviral copies/10(3) PBMCs were detected in group I versus group II (75.4 +/- 104.3 and 13.0 +/- 17.8 respectively, p < 0.0001) and in RP (158.0 +/- 118.2) as compared to either SP (11.8 +/- 18.8, p < 0.0001) or other age-matched infected children (20.3 +/- 38.8, p < 0.0001). Thus HIV-infected children appear to have a higher cell-associated virus load early in life, especially in association with rapid disease progression. 相似文献
32.
Empirical studies suggest a very high prevalence of atopic disorder in people with depression. Research indicates that individuals with allergy have cholinergic hyperresponsiveness and beta-adrenergic hyporesponsiveness in the autonomic nervous system. Evidence is reviewed that similar imbalances in CNS cholinergic–adrenergic activity play a causal role in depression behaviors. It is hypothesized that the allergic state or allergic reactions can accentuate cholinergic–adrenergic activity imbalances in the CNS of a small subgroup of people at risk for endogenous depression thereby producing depression symptomatology. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
33.
Packaging engineers need to be able to accurately determine the forces present in the shipping environment in order to protect packaged goods. The purpose of this study was to determine the vertical vibration levels measured in three separate truck-trailer suspension systems; conventional leaf-spring, conventional air-ride and damaged air-ride. The main conclusion reached in this study is that the air-ride suspension when maintained gives lower power density (PD) levels on all road surfaces studied. A damaged air-ride suspension and leaf-spring suspension are very similar in response frequencies, although the damaged air-ride produces higher vibration levels at lower frequencies. 相似文献
34.
Ellen Y. Sun Kathleen B. Alexander Paul F. Becher Shyh-Lung Hwang 《Journal of the American Ceramic Society》1996,79(10):2626-2632
Interfacial microstructures in βP-Si3 N4 ( w )-Si-Al-Y-O-N-glass systems were investigated by systematically varying the nitrogen content and the Al:Y ratio of the glass matrix. High-resolution and analytical transmission electron microscopy (HREM and AEM) studies revealed that the interfacial microstructure is a function of the glass composition. No interfacial phases were formed in glasses with low Al:Y ratios and in glasses with high Al:Y ratios and low nitrogen content, whereas epitaxial growth of an interfacial layer (100–200 μm thick) on the βP-Si3 N4 ( w ) occurred in a glass matrix with high Al:Y ratio and high nitrogen content. The interfacial layer was identified to be a β'-SiAION phase. Interfaces containing the SiAION layer exhibited high debonding energy compared to Si3 N4 ( w )–glass interfaces. HREM studies indicated that the lattice-mismatch strain in the SiAION layer was relieved by dislocation formation at the SiAION–Si3 N4 ( w ) interface. The difference in interfacial debonding energy was, hence, attributed to the local atomic structure and bonding between the glass-β-Si3 N4 and the glass–β'-SiAION phases. This observation was clear evidence of the strong influence of glass chemistry on the interfacial debonding behavior by altering the interfacial microstructure. 相似文献
35.
36.
37.
38.
39.
Sven Beyer Christian Jacobi Daniel Kröning Dirk Leinenbach Wolfgang J. Paul 《International Journal on Software Tools for Technology Transfer (STTT)》2006,8(4-5):411-430
In the verified architecture microprocessor (VAMP) project we have designed, functionally verified, and synthesized a processor
with full DLX instruction set, delayed branch, Tomasulo scheduler, maskable nested precise interrupts, pipelined fully IEEE
compatible dual precision floating point unit with variable latency, and separate instruction and data caches. The verification
has been carried out in the theorem proving system PVS. The processor has been implemented on a Xilinx FPGA.
A shorter version of this article with the title “Instantiating uninterpreted functional units and memory system: functional
verification of the VAMP” appeared in [8]. The work reported here was done while all the authors were with Saarland University. 相似文献
40.
Examined the job performance of 420 credit managers (mean age at hiring 25 yrs) from a large finance company who either quit their job, were fired, or were promoted to a higher position in the company. Six biographical variables and 12 performance appraisal scores accumulated from data in employee files were used in a cross-validated multiple discriminant analysis to predict membership in the 3 classification groups. Results reveal a systematic relation between the performance appraisal variables and the classification groups: The performance of promoted Ss was significantly superior to that of Ss who quit, which in turn was significantly superior to the performance of the fired Ss. 18 discriminating variables accounted for a 46.7% hit rate in group membership. Findings are discussed in the context of research on performance antecedents of voluntary and involuntary turnover, as well as the feedback properties of performance appraisal information. It is suggested that no single performance–turnover relation exists. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献