全文获取类型
收费全文 | 3818篇 |
免费 | 11篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 71篇 |
金属工艺 | 11篇 |
机械仪表 | 7篇 |
建筑科学 | 40篇 |
能源动力 | 15篇 |
轻工业 | 76篇 |
水利工程 | 12篇 |
石油天然气 | 2篇 |
无线电 | 72篇 |
一般工业技术 | 91篇 |
冶金工业 | 3356篇 |
原子能技术 | 3篇 |
自动化技术 | 61篇 |
出版年
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2016年 | 7篇 |
2015年 | 15篇 |
2014年 | 6篇 |
2013年 | 17篇 |
2012年 | 12篇 |
2011年 | 25篇 |
2010年 | 16篇 |
2009年 | 21篇 |
2008年 | 30篇 |
2007年 | 23篇 |
2006年 | 20篇 |
2005年 | 17篇 |
2004年 | 20篇 |
2003年 | 18篇 |
2002年 | 8篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 123篇 |
1998年 | 1109篇 |
1997年 | 631篇 |
1996年 | 432篇 |
1995年 | 221篇 |
1994年 | 170篇 |
1993年 | 208篇 |
1992年 | 16篇 |
1991年 | 45篇 |
1990年 | 48篇 |
1989年 | 47篇 |
1988年 | 40篇 |
1987年 | 33篇 |
1986年 | 24篇 |
1985年 | 18篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 29篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 70篇 |
1976年 | 138篇 |
1975年 | 5篇 |
1973年 | 6篇 |
1942年 | 4篇 |
1940年 | 8篇 |
1938年 | 5篇 |
排序方式: 共有3829条查询结果,搜索用时 0 毫秒
11.
CJ Reid 《Canadian Metallurgical Quarterly》1993,7(3):327-328
The results of a retrospective study of routine measurement of haemoglobin at the examination of one-year-old children at Gr?land mother and child clinic during 1989-91 showed that 37% of the children had anaemia. There was no difference between immigrants and the European population. There was no correlation between anaemia and sex in either of the population groups. This may imply that routine haemoglobin measurement should be generally introduced as part of the regular control of one-year-old children. 相似文献
12.
ED Schneiderman SM Willis CJ Kowalski TR Ten have 《Canadian Metallurgical Quarterly》1993,32(1):35-43
Sixty-five patients initially seropositive for IgM anti-phenolic glycolipid-I (PGL-I) antibodies were tested for antibody levels to PGL-I, lipoarabinomannan (LAM), and the 35-kDa protein of Mycobacterium leprae at regular intervals for up to 30 months following the commencement of multidrug therapy (MDT). There was a steady decline in IgM anti-PGL-I and anti-35-kDa antibody levels to a mean of 17% and 14%, respectively, of the starting level at 24 months. The development of type 1 and type 2 reactions or the presence of drug-resistant organisms in a small number of patients had no significant influence on the changes in antibody level. The rate of decline was similar in different disease categories, but a higher proportion of lepromatous patients remained seropositive at the end of 2 years of treatment than borderline tuberculoid patients. By contrast, the mean IgG anti-LAM antibody levels remained stable or increased. Again the occurrence of type 1 or type 2 reactions had no significant effect on antibody level over 2 years. Falls in the IgM anti-PGL-I antibody levels mirrored the falls in the bacterial index in individual patients and provide an additional parameter for monitoring the response to chemotherapy. 相似文献
13.
14.
A deletion mutant of the catalytic RNA component of Escherichia coli RNase P missing residues 87-241 retains the ability to interact with the protein component to form a functional catalyst. The deletion of this phylogenetically conserved region significantly increases the Km, indicating that the deleted structures may be important for binding to the precursor tRNA substrate but not for the cleavage reaction. Under some reaction conditions, this RNase P deletion mutant can become a relatively non-specific nuclease, indicating that this RNA's catalytic center may be more exposed. The catalytic core of the RNase P is formed by less than one third of the 377 residues of the RNase P RNA. 相似文献
15.
16.
17.
18.
Shiga-like toxin I (SLT-I), the potent cytotoxin produced by certain pathogenic strains of Escherichia coli, is a member of a burgeoning family of ribosome-in-activating proteins (RIPs), which share common structural and mechanistic features. The prototype of the group is the plant toxin ricin. Recently we proposed a structural model for the Slt-IA active site, based in part on the known geometry of the enzymatic subunit of the ricin toxin. The model places three aromatic residues within the putative Slt-IA active site cleft: tyrosine 77, tyrosine 114, and tryptophan 203. Here we present biochemical and biophysical data regarding, the phenotypes of conservative point mutants of Slt-IA in which tyrosine 114 is altered. We used oligonucleotide-directed mutagenesis to replace tyrosine 114 with either phenylalanine (Y114F) or serine (Y114S). Periplasmic extracts of E. coli containing wild-type or mutant Slt-IA were tested for their ability to inhibit protein synthesis in vitro. Relative to wild-type, the activity of mutant Y114F was attenuated about 30-fold, while the mutant Y114S was attenuated about 500 to 1000-fold. In order to address the possibility that differential activation of the mutants rather than local effects at the active site might account for their diminished activity, we engineered the same mutations into a truncated slt-IA cassette that directs expression of a product corresponding to the activated A1 form of Slt-IA (wild-type-delta). The same general relationships held: relative to wild type-delta, Y114F-delta was attenuated about 7-fold, and Y114S-delta about 300-fold.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
19.
JH Viles JB Mitchell SL Gough PM Doyle CJ Harris PJ Sadler JM Thornton 《Canadian Metallurgical Quarterly》1996,242(2):352-362
The aqueous solution structure of the cyclic pentapeptide cyclo(-Ser-D-Leu-Asp-Val-Pro-) has been determined by two-dimensional 1H-NMR spectroscopy, combined with a conformational search and distance-geometry calculations. As many as five conformers in slow exchange were observed, and the rate of interconversion between components was measured from the build-up rates of exchange peaks. NMR data allowed the structures of the two predominant conformers to be determined. The major component (66%) contained a cis-proline as part of a type-VIa2 beta-turn encompassing residues Asp-Val-cis-Pro-Ser. The second component (16%) contained only trans-amide bonds, and a type-VIII beta-turn formed by residues Val-Pro-Ser-D-Leu. These structures are discussed in relation to the (phi, psi), space available to the cyclic pentapeptide, determined by a conformational search, and in relation to previously published cyclic-pentapeptide structures. The molecule exhibits activity in a scintillation-proximity assay for the inhibition of the interaction between the integrin very-late antigen-4 (VLA-4; alpha 4 beta 1) and vascular-cell-adhesion molecule-1 (VCAM-1). The structure/activity relationship of the LDV sequence is discussed and related to the recently published X-ray structure of VCAM-1. The relevance of the work to the design of anti-inflammatory drugs is discussed. 相似文献
20.