全文获取类型
收费全文 | 5585篇 |
免费 | 250篇 |
国内免费 | 27篇 |
专业分类
化学 | 4551篇 |
晶体学 | 58篇 |
力学 | 85篇 |
数学 | 588篇 |
物理学 | 580篇 |
出版年
2023年 | 33篇 |
2022年 | 77篇 |
2021年 | 75篇 |
2020年 | 85篇 |
2019年 | 92篇 |
2018年 | 68篇 |
2017年 | 52篇 |
2016年 | 143篇 |
2015年 | 152篇 |
2014年 | 170篇 |
2013年 | 315篇 |
2012年 | 388篇 |
2011年 | 429篇 |
2010年 | 227篇 |
2009年 | 239篇 |
2008年 | 404篇 |
2007年 | 377篇 |
2006年 | 342篇 |
2005年 | 345篇 |
2004年 | 304篇 |
2003年 | 235篇 |
2002年 | 263篇 |
2001年 | 80篇 |
2000年 | 59篇 |
1999年 | 69篇 |
1998年 | 50篇 |
1997年 | 52篇 |
1996年 | 65篇 |
1995年 | 45篇 |
1994年 | 43篇 |
1993年 | 36篇 |
1992年 | 45篇 |
1991年 | 38篇 |
1990年 | 33篇 |
1989年 | 37篇 |
1988年 | 22篇 |
1987年 | 19篇 |
1986年 | 27篇 |
1985年 | 32篇 |
1984年 | 26篇 |
1983年 | 24篇 |
1982年 | 33篇 |
1981年 | 15篇 |
1980年 | 25篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 22篇 |
1976年 | 25篇 |
1975年 | 18篇 |
1974年 | 13篇 |
排序方式: 共有5862条查询结果,搜索用时 171 毫秒
1.
2.
3.
4.
Fundamental processes in long air gap discharges 总被引:2,自引:0,他引:2
I. Gallimberti G. Bacchiega Anne Bondiou-Clergerie Philippe Lalande 《Comptes Rendus Physique》2002,3(10):854
The development of atmospheric lightning is initiated and sustained by the formation in virgin air of ‘streamer corona’ and ‘leader’ discharges, very similar to those observed in laboratory long sparks. Therefore, the experimental and theoretical investigations of these laboratory discharges have become of large interest to improve the physical knowledge of the lightning process and to develop self-consistent models that could be applied to new protection concepts.In the present paper the fundamental processes of the subsequent phases of long air gap discharges are analyzed, from the first corona inception and development to the leader channel formation and propagation. For all these processes simulations models are discussed that have been essentially derived and simplified by the authors, in order to develop sequential time-dependent simulation of the laboratory breakdown, with both positive and negative voltages. The possibility of extending these models to the case of natural lightning is discussed in the companion paper, presented in this same volume. To cite this article: I. Gallimberti et al., C. R. Physique 3 (2002) 1335–1359. 相似文献
5.
6.
Sulfate-reducing bacteria (SRB) were isolated from anaerobic sludge of yeast factory wastewater treatment plant by cultivation on Postgate C medium. Microcalorimetry was used to monitor the anaerobic digestion processes and to measure the growth rates of sulfate-reducing bacteria. The maximum growth rates determined by microcalorimetry and ATP analysis were different—μmax(dQ/dt) = 0.165 ± 0.008 h−1 and μmax(NATP) = 0.207 ± 0.013 h−1. Experiments on the cultivation of SRB from yeast industry wastewater treatment plant in batch culture showed that during the first 20 h the concentration of sulfate decreased from 78.3 mM down to 62.2 mM while the increase of sulfide production was negligible. Perceptible amount of sulfide (7.82 mM) appeared on the 33.5 h of fermentation together with a peak on the power–time curve and considerable increase in the cell count (1.26 × 109). First steps of sulfate metabolism (activation of sulfate by ATP sulfurylase, production of H2) are accompanied by endothermic heat effects, therefore the values of thermal power remain moderate until the evolution of sulfide starts. The influence of green microalgae Chlorococcum sp. (preparation Biotreat 100) on the growth characteristics of microorganisms was also studied. Identification of one SRB strain was started by sequencing of PCR-amplified 16S rRNA gene. Two sets of primers were used for PCR amplification, both specific for domain Bacteria but giving different gene fragments. PCR-products were purified with JETQUICK kit according to the manufacturer instructions. 相似文献
7.
Jonathan L. Sessler Patricia J. Melfi Anne E.V. Gorden Doris K. Ford C. Drew Tait 《Tetrahedron》2004,60(49):11089-11097
Hexaphyrin(1.0.1.0.0.0) (isoamethyrin) undergoes a significant color change in the presence of UO22+, PuO22+, and NpO22+. The complexation of the first of these dioxo actinide cations was studied in semi-quantitative fashion in 1:1 MeOH-CH2Cl2. Under these conditions, the detection limit for UO22+ was found to be ca. 5.8 ppm by naked eye monitoring and <28 ppb by UV-vis spectroscopy. Isoamethyrin does not undergo a color change in the presence of most transition metals or when exposed to Gd(III). Isoamethyrin thus constitutes an attractive alternative to 2,2′(1,8-dihydroxy-3,6-disulfonaphthylene-2,7-bisazo)-bisbenzenarsonic acid (AzIII) and 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (BrPADAP), systems currently used as actinide cation sensors. 相似文献
8.
Optimization of the Heck reaction of 4-bromoacetophenone with styrene by a polymer supported, sulfur-containing palladacycle, varying 6 factors at a total of 28 different levels, corresponding to 5760 different possibilities was undertaken. Conversion improved from 34%, with large observable leaching to 88% with no leaching. This was accomplished using a Design of Experiments approach facilitated by the Statistical Design Package, MODDE 7.0TM. 相似文献
9.
Anne Buschmann Ute Ziegler Martin H. Groschup 《Accreditation and quality assurance》2004,9(4-5):191-197
The accumulation of pathological prion protein is used as a diagnostic marker for transmissible spongiform encephalopathies. According to European Union (EU) regulations cattle older than 30 months of age (Germany, France, Italy, and Spain by national law >24 months) and slaughtered for human consumption must be tested by using rapid tests for bovine spongiform encephalopathy (BSE). Likewise fallen stock and clinically affected animals must be tested. This article gives a short overview of the incidence of BSE in Europe. The diagnostic hierarchy, i.e., the officially approved methodology for the confirmation of suspect rapid test cases, and the organization of the numerous laboratories involved in this large-scale testing for BSE are described. Special emphasis is given to necessary quality control measures currently in place for BSE rapid testing laboratories and to measures intended to assure a consistent performance of the commercially available rapid test kits.Presented at BERM-9—Ninth International Symposium on Biological and Environmental Reference Materials, 15–19 June 2003, Berlin, Germany. 相似文献
10.