全文获取类型
收费全文 | 2235篇 |
免费 | 32篇 |
专业分类
电工技术 | 12篇 |
综合类 | 1篇 |
化学工业 | 301篇 |
金属工艺 | 7篇 |
机械仪表 | 22篇 |
建筑科学 | 35篇 |
矿业工程 | 1篇 |
能源动力 | 18篇 |
轻工业 | 114篇 |
水利工程 | 10篇 |
无线电 | 83篇 |
一般工业技术 | 160篇 |
冶金工业 | 1394篇 |
原子能技术 | 20篇 |
自动化技术 | 89篇 |
出版年
2023年 | 9篇 |
2022年 | 17篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 15篇 |
2016年 | 14篇 |
2015年 | 21篇 |
2014年 | 14篇 |
2013年 | 31篇 |
2012年 | 26篇 |
2011年 | 41篇 |
2010年 | 33篇 |
2009年 | 40篇 |
2008年 | 42篇 |
2007年 | 37篇 |
2006年 | 32篇 |
2005年 | 22篇 |
2004年 | 23篇 |
2003年 | 33篇 |
2002年 | 21篇 |
2001年 | 24篇 |
2000年 | 17篇 |
1999年 | 50篇 |
1998年 | 424篇 |
1997年 | 235篇 |
1996年 | 173篇 |
1995年 | 88篇 |
1994年 | 82篇 |
1993年 | 75篇 |
1992年 | 33篇 |
1991年 | 24篇 |
1990年 | 21篇 |
1989年 | 26篇 |
1988年 | 34篇 |
1987年 | 26篇 |
1986年 | 29篇 |
1985年 | 30篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1978年 | 22篇 |
1977年 | 49篇 |
1976年 | 122篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有2267条查询结果,搜索用时 31 毫秒
11.
J Weber P Majer J Litera J Urban M Soucek J Vondrásek J Konvalinka P Novek J Sedlácek P Strop HG Kr?usslich I Pichová 《Canadian Metallurgical Quarterly》1997,341(1):62-69
The results of investigation of haptoglobin (Hp) types in 596 donor blood samples in some towns of Ukraine (Dnepropetrovsk, Kharkov, Odessa, Kiev, Uzhgorod, Zhitomir) are presented. Three normal Hp types (Hp1-1, Hp2-1 and Hp2-2) have been found. The reliable interpopulation differences in the Hp types frequency were not found. On the whole the Hp types frequency in the type Hp1-1 comprised 12.7%. In the type Hp2-1-48.1% and in the type Hp2-2-36.5%. The frequency of the gene Hp1 is 0.38. The frequency of the Hp types and of the gene Hpl in Ukraine is similar to that in population of Eastern Europe and European Part of Russia. 相似文献
12.
HG Morrison EJ Weil SI Karchner ML Sogin JJ Stegeman 《Canadian Metallurgical Quarterly》1998,121(1-3):231-240
Since we published a phylogenetic analysis of the CYP1A subfamily in 1995, several additional full-length sequences have been reported, including three members of an entirely new subfamily, CYP1B. Two avian sequences were recently published, so that CYP1A sequence data are now available from three of the five major vertebrate lineages. The two new branches that have been added to the CYP1 family tree significantly add to our understanding of P450 evolution. The inclusion of the CYP1Bs to the phylogenetic analysis allows us to root inferred trees. Addition of the avian CYP1As indicates that the CYP1A1/CYP1A2 duplication present in the mammalian lineage may have occurred after the divergence of birds and mammals. The number of fish species from which full-length coding regions of CYP1A genes have been sequenced has increased from four (trout, plaice, toadfish, and scup) to nine. These include CYP1A sequences from tomcod, butterflyfish, sea bream, sea bass, and the full-length sequence of CYP1A from the killifish Fundulus heteroclitus that is reported here. Phylogenetic analyses incorporating the new fish CYP1A sequences support our original conclusion that the fish CYP1As are monophyletic and indicate that the genes are evolving at very different rates in different species. 相似文献
13.
The barrier function, surface biochemistry, and morphology of confluent monolayers of endothelial cells isolated from different segments of the bovine lung vasculature [microvessels (BLMVEC), vein (BPVEC) and artery (BPAEC)] were grown in culture and compared. A number of common cell surface proteins were identified along with two proteins of 46 and 48 kDa found exclusively on BPVEC. Lectin affinity chromatography revealed multiple glycosylation differences. The lectins, Arachis hypogaea (AHA) and Lycopersicum esculentum (LEA) agglutinins, interacted with several glycoproteins of BLMVEC but not of BPAEC. Bandeiraea simplicifolia (BS-1) and Caragana arborescens (CAA) agglutinins recognized several glycoproteins of BPVEC and BPAEC but not BLMVEC. Permeabilities were much lower for BLMVEC than BPAEC or BPVEC monolayers, with a range of about 16-fold less for sucrose to 2-fold less for albumin. Electron microscopy revealed that BLMVEC have a greater surface density of plasmalemmal vesicles (approximately 4-fold) and more extensively developed intercellular junctions with more focal membrane adhesion sites per junction (approximately 9-fold) than the other cells. We conclude that: i) BLMVEC monolayers form a much more restrictive barrier to molecular transport as a result of the tighter junctional formation; and ii) endothelial surface glycoproteins may be differentially glycosylated depending on their segmental location within the vasculature. 相似文献
14.
We have previously shown that strychnine mimics the cytoprotective properties of glycine in renal proximal tubule (RPT) suspensions exposed to antimycin A (AA). The aims of this study were to determine whether the cytoprotective properties of strychnine applied to various types of nephrotoxicants and to examine the temporal aspects of the cytoprotection of glycine and strychnine. Tubular release of LDH activity was used as a marker of cell death. Glycine (2 mM) or strychnine (1 mM) added 5 min prior to the toxicant decreased LDH release in rabbit RPT suspensions exposed to 25 microM tetrafluoroethyl-L-cysteine (TFEC), 10 microM HgCl2, 0.5 mM t-butyl hydroperoxide (TBHP), or 0.2 mM bromohydroquinone (BHQ) for 4 hr, or 2 mM sodium cyanide (NaCN) for 2 hr. The relative rank order of effectiveness of glycine and strychnine was NaCN = TFEC > BHQ > DCVC > TBHP > HgCl2. The temporal aspects of strychnine and glycine protection were examined by exposing RPT to either AA or TFEC for 1 or 3 hr, respectively, and then adding either 1 mM glycine or 1 mM strychnine. Glycine and strychnine decreased LDH release in AA-treated RPT at 1.25 and 2 hr and TFEC-treated RPT at 4 hr. In addition, when RPT exposed to AA or TFEC and treated with strychnine or glycine were washed at either 1 or 4 hr, protection was eliminated at later time points. When glycine was added to RPT treated with either PCBC, TFEC, or DCVC 5 min prior to or 30, 60, 120, and 180 min following toxicant addition, LDH release was reduced at all time points. These results demonstrate that strychnine and glycine protect RPT from a variety of diverse nephrotoxicants, strychnine and glycine do not need to be present at the time of toxic insult, strychnine and glycine cytoprotection is reversible, and strychnine and glycine act in the late phase of necrotic cell injury. 相似文献
15.
16.
17.
In Experiment 1, a group of listeners with substantial hearing loss due to presbyacusis and a group of listeners with normal hearing were given three localization tests: a frontal plane test in which they judged whether sounds came from the left, overhead, or the right; a sagittal plane test in which they judged whether sounds came from directly in front, overhead, or behind; and an elevation test in which they judged the vertical position of sounds coming from in front. The two groups performed similarly on the frontal plane test, which chiefly depended upon their ability to use binaural localization cues. They performed differently on the sagittal plane and elevation tests, for which the predominant localization cues were spectral. The listeners with presbyacusis were substantially less accurate than those with normal hearing in both of these instances. They had particular difficulty judging source elevation, rarely scoring much above chance. Follow-up testing of a group of subjects in the early stages of presbyacusis showed localization performance that was intermediate to the other two groups, but far more like that of the normal-hearing listeners. In Experiment 2, additional tests were run with the following conditions designed to encourage improved performance by listeners with presbyacusic hearing loss: (1) filtering of stimuli to preclude masking of more informative high-frequency components by low frequencies; (2) simplification of the elevation test and greater spatial separation of its loudspeaker sources; and (3) use of hearing aids. Conditions 1 and 2 had no appreciable effect on performance; condition 3 significantly improved presbyacusic listeners' ability to localize in the sagittal plane, particularly when sounds came from the front. 相似文献
18.
19.
20.