全文获取类型
收费全文 | 5272篇 |
免费 | 37篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 13篇 |
综合类 | 6篇 |
化学工业 | 232篇 |
金属工艺 | 44篇 |
机械仪表 | 48篇 |
建筑科学 | 26篇 |
矿业工程 | 2篇 |
能源动力 | 22篇 |
轻工业 | 440篇 |
水利工程 | 3篇 |
石油天然气 | 1篇 |
无线电 | 155篇 |
一般工业技术 | 244篇 |
冶金工业 | 3894篇 |
原子能技术 | 33篇 |
自动化技术 | 148篇 |
出版年
2021年 | 23篇 |
2018年 | 20篇 |
2016年 | 28篇 |
2014年 | 25篇 |
2013年 | 38篇 |
2012年 | 44篇 |
2011年 | 45篇 |
2010年 | 34篇 |
2009年 | 36篇 |
2008年 | 52篇 |
2007年 | 55篇 |
2006年 | 41篇 |
2005年 | 43篇 |
2004年 | 47篇 |
2003年 | 33篇 |
2002年 | 43篇 |
2001年 | 47篇 |
2000年 | 30篇 |
1999年 | 157篇 |
1998年 | 1319篇 |
1997年 | 688篇 |
1996年 | 477篇 |
1995年 | 233篇 |
1994年 | 224篇 |
1993年 | 217篇 |
1992年 | 55篇 |
1991年 | 54篇 |
1990年 | 62篇 |
1989年 | 74篇 |
1988年 | 65篇 |
1987年 | 52篇 |
1986年 | 50篇 |
1985年 | 57篇 |
1984年 | 19篇 |
1983年 | 22篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1980年 | 38篇 |
1978年 | 18篇 |
1977年 | 77篇 |
1976年 | 165篇 |
1912年 | 15篇 |
1911年 | 15篇 |
1910年 | 26篇 |
1909年 | 36篇 |
1908年 | 26篇 |
1907年 | 50篇 |
1906年 | 33篇 |
1905年 | 44篇 |
1904年 | 49篇 |
排序方式: 共有5311条查询结果,搜索用时 281 毫秒
1.
Sebastian Roth Peter Stockinger Jakob Steff Simon Steimle Dr. Viktor Sautner Prof. Dr. Kai Tittmann Prof. Dr. Jürgen Pleiss Prof. Dr. Michael Müller 《Chembiochem : a European journal of chemical biology》2020,21(18):2615-2619
The family of NAD(P)H-dependent short-chain dehydrogenases/reductases (SDRs) comprises numerous biocatalysts capable of C=O or C=C reduction. The highly homologous noroxomaritidine reductase (NR) from Narcissus sp. aff. pseudonarcissus and Zt_SDR from Zephyranthes treatiae, however, are SDRs with an extended imine substrate scope. Comparison with a similar SDR from Asparagus officinalis (Ao_SDR) exhibiting keto-reducing activity, yet negligible imine-reducing capability, and mining the Short-Chain Dehydrogenase/Reductase Engineering Database indicated that NR and Zt_SDR possess a unique active-site composition among SDRs. Adapting the active site of Ao_SDR accordingly improved its imine-reducing capability. By applying the same strategy, an unrelated SDR from Methylobacterium sp. 77 (M77_SDR) with distinct keto-reducing activity was engineered into a promiscuous enzyme with imine-reducing activity, thereby confirming that the ability to reduce imines can be rationally introduced into members of the “classical” SDR enzyme family. Thus, members of the SDR family could be a promising starting point for protein approaches to generate new imine-reducing enzymes. 相似文献
2.
Using an integrated process of data and modeling in HRA 总被引:1,自引:0,他引:1
John Wreathall Dennis Bley Emilie Roth Jordan Multer Thomas Raslear 《Reliability Engineering & System Safety》2004,83(2):221
The paper describes an approach taken to estimate the probabilities of failure associated with various railroad tasks to prevent accidents (principally collisions and derailments). These probabilities were estimated using an expert elicitation process that used partially relevant data available from a variety of databases and that were filtered and scaled to make them more directly relevant to the analyses being performed. Extensive qualitative studies were performed prior to the elicitation process to identify relevant contexts under which the tasks can be performed. 相似文献
3.
J.M. Roth T.G. Ulmer N.W. Spellmeyer S. Constantine M.E. Grein 《Photonics Technology Letters, IEEE》2004,16(9):2009-2011
We demonstrate a novel 40-GHz mode-locked fiber laser that utilizes a single active device to provide both gain and mode-locking. The laser produces pulses as short as 2.2 ps, is tunable over a 27-nm band centered at 1553 nm, and exhibits long-term stability without cavity-length feedback control. The pulse train at 1556 nm was used in a 40-Gb/s transmission experiment over 45 km with a low 0.4-dB power penalty. 相似文献
4.
5.
Antibiotic treatment options for Burkholderia cepacia infection are limited because of high intrinsic resistance. The problem is complicated by development of cross-resistance between antibiotics of different classes. We isolated antibiotic-resistant mutants by stepwise exposure to chloramphenicol (Chlor) and to trimethoprim/sulphamethoxazole (T/S) for four B. cepacia strains: ATCC13945, Per (clinical isolate), Cas and D4 (environmental isolates). Chlor(r) mutants did not produce chloramphenicol acetyl-transferase. Cross-resistance, defined as greater than four-fold increase in MIC by microtitre dilution method, was consistently seen in both types of mutants. For chloramphenicol-resistant (Chlor[r]) and trimethoprim/sulphamethoxazole-resistant (Tr/Sr) mutants of B. cepacia ATCC13945 and Cas, no MIC change was seen for piperacillin, ceftazidime, rifampicin, gentamicin, tobramycin, polymyxin B or azithromycin. B. cepacia-Per and -D4 mutants showed cross-resistance to ceftazidime and to piperacillin. Comparison of outer membrane protein (OMP) profiles of B. cepacia and their mutants by SDS-PAGE revealed Tr/Sr) mutants to be deficient in a major OMP (molecular weight 39-47 kDa). Tr/Sr mutants also expressed additional OMPs not found in wild type strains at 75-77 kDa for B. cepacia-ATCC13945 and -Cas, and 20-21 kDa in B. cepacia-D4 and -Per. No OMP changes occurred in Chlor(r) mutants. Lipopolysaccharide (LPS) profiles of each type of mutant showed new high and low molecular weight LPS bands. Cross-resistance seems to be mediated by alterations in porin and LPS for Tr/Sr mutants, but only by LPS in Chlor(r) mutants. 相似文献
6.
Vertical phoria (vertical vergence in the absence of binocular feedback) can be trained to vary with non-visual cues such as vertical conjugate eye position, horizontal conjugate eye position and horizontal vergence. These prior studies demonstrated a low-level association or coupling between vertical vergence and several oculomotor cues. As a test of the potential independence of multiple eye-position cues for vertical vergence, context-specific adaptation experiments were conducted in three orthogonal adapting planes (midsagittal, frontoparallel, and transverse). Four vertical disparities in each of these planes were associated with various combinations of two specific components of eye position. Vertical disparities in the plane were associated with horizontal vergence and vertical conjugate eye position; vertical disparities in the frontoparallel plane were associated with horizontal and vertical conjugate eye position; and vertical disparities in the transverse plane were associated with horizontal vergence and horizontal conjugate eye position. The results demonstrate that vertical vergence can be adapted to respond to specific combinations of two different sources of eye-position information. The results are modeled with an association matrix whose inputs are two classes of eye position and whose weighted output is vertical vergence. 相似文献
7.
8.
9.
10.
M Ramirez-Salomon R Soler-Bientz R de la Garza-González CM Palacios-Garza 《Canadian Metallurgical Quarterly》1997,23(9):586-587
It is important for endodontic instruments to have a low fracture rate. If a fracture does occur, it would be desirable to have the ability to bypass the broken segment and complete the root canal treatment. One hundred sixty-two root canals in 52 maxillary and mandibular first molars were cleaned and shaped with Lightspeed instruments by three endodontists in their private practices. The canals were instrumented using the technique recommended by the manufacturer. All canals were instrumented to at least a size 45 at the working length. Six instruments separated during treatment. All six had been used more times than recommended by the manufacturer. Five of the six were easily bypassed and treatment completed. 相似文献