全文获取类型
收费全文 | 1372篇 |
免费 | 69篇 |
国内免费 | 8篇 |
专业分类
化学 | 1115篇 |
晶体学 | 9篇 |
力学 | 27篇 |
数学 | 175篇 |
物理学 | 123篇 |
出版年
2023年 | 13篇 |
2022年 | 19篇 |
2021年 | 22篇 |
2020年 | 23篇 |
2019年 | 31篇 |
2018年 | 17篇 |
2017年 | 10篇 |
2016年 | 37篇 |
2015年 | 39篇 |
2014年 | 44篇 |
2013年 | 77篇 |
2012年 | 71篇 |
2011年 | 118篇 |
2010年 | 56篇 |
2009年 | 61篇 |
2008年 | 88篇 |
2007年 | 108篇 |
2006年 | 95篇 |
2005年 | 84篇 |
2004年 | 76篇 |
2003年 | 48篇 |
2002年 | 42篇 |
2001年 | 14篇 |
2000年 | 20篇 |
1999年 | 24篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 26篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1978年 | 4篇 |
1974年 | 5篇 |
1972年 | 2篇 |
1940年 | 2篇 |
1939年 | 4篇 |
1930年 | 2篇 |
排序方式: 共有1449条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
Photo-reductive dehalogenation of aromatic halides to their parent hydrocarbons is stimulated in the presence of electron donors such as di-ethyl sulphide. Evidence is presented for the involvement of radicals ions in these reactions. 相似文献
95.
Ondeykal JG Herath KB Jayasuriya H Polishook JD Bills GF Dombrowski AW Mojena M Koch G DiSalvo J DeMartino J Guan Z Nanakorn W Morenberg CM Balick MJ Stevenson DW Slattery M Borris RP Singh SB 《Molecular diversity》2005,9(1-3):123-129
The chemokines (CXCL9, CXCL10 and CXCL11) and associated CXCR3 receptor are expressed during the inflammatory process from multiple sclerosis, atherosclerosis or organ transplantation resulting in the recruitment of lymphocytes leading to tissue damage. It is hypothesized that blocking of the ligand/CXCR3 receptor interaction has potential to provide opportunity for development of agents that would block tissue rejection. In this paper, four classes of natural product inhibitors (IC50 ranging 0.1–41 M) have been described that block the CXCR3 receptor interaction of IP-10 ligand. These include a cyclic thiopeptide (duramycin), polyketide glycosides (roselipins), steroidal glycosides (hypoglausin A and dioscin) and a novel alkyl pyridinium alkaloid that were isolated by bioassay-guided fractionation of the organic extracts derived from actinomycete, fungal, plant and marine sources and discovered using 125 I IP-10/CXCR3 binding assay. Duramycin was the most potent with an IC50 of 0.1 M. Roselipins 2A, 2B and 1A showed IC50 values of 14.6, 23.5, and 41 M, respectively. Diosgenin glycosides dioscin, hypoglaucin A and kallstroemin D exhibited IC50 values of 2.1, 0.47 and 3 M, respectively. A novel cyclic 3-alkyl pyridinium salt isolated from a sponge displayed a binding IC50 of 0.67 M. 相似文献
96.
The magnetic study of a trinuclear Cu-Gd-Cu complex confirms that such basic units self-assemble to yield a high spin species. A nice fit of the magnetic data is obtained for an infinite chain of tetranuclear Gd(2)Cu(2) motifs linked through the Gd ions located at the opposite vertexes of the tetranuclear motifs according to two Cu-Gd coordination modes, a double bridging through phenoxo and alkoxo oxygen atoms and a single bridging through deprotonated amide functions. The two interaction pathways are ferromagnetic. Alternating current susceptibility measurements confirm that the equivalent copper-terbium entity is a single chain magnet with a barrier height for reversal of the magnetization equal to 28.5 K. 相似文献
97.
Because many cetacean species produce characteristic calls that propagate well under water, acoustic techniques can be used to detect and identify them. The ability to identify cetaceans to species using acoustic methods varies and may be affected by recording and analysis bandwidth. To examine the effect of bandwidth on species identification, whistles were recorded from four delphinid species (Delphinus delphis, Stenella attenuata, S. coeruleoalba, and S. longirostris) in the eastern tropical Pacific ocean. Four spectrograms, each with a different upper frequency limit (20, 24, 30, and 40 kHz), were created for each whistle (n = 484). Eight variables (beginning, ending, minimum, and maximum frequency; duration; number of inflection points; number of steps; and presence/absence of harmonics) were measured from the fundamental frequency of each whistle. The whistle repertoires of all four species contained fundamental frequencies extending above 20 kHz. Overall correct classification using discriminant function analysis ranged from 30% for the 20-kHz upper frequency limit data to 37% for the 40-kHz upper frequency limit data. For the four species included in this study, an upper bandwidth limit of at least 24 kHz is required for an accurate representation of fundamental whistle contours. 相似文献
98.
Sur UK Marken F Coles BA Compton RG Dupont J 《Chemical communications (Cambridge, England)》2004,(24):2816-2817
Self-focusing of intense microwave radiation at the tip of a 25 microm diameter platinum disk microelectrode immersed into the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM(+)PF(6)(-)) containing 1 mM ferrocene causes dramatically (two orders of magnitude) enhanced voltammetric current signals and temperatures in excess of 600 K (at the electrode surface)--extreme conditions sufficient for condensed phase pyrolysis processes to occur. 相似文献
99.
An electrospray ionization mass spectrometry based assay was developed for kinetic measurements and inhibitor screening of yeast hexokinase. There is considerable discrepancy in the literature as to the accuracy of kinetic data obtained for hexokinase. In the assay described herein, the product, glucose 6-phosphate was directly monitored by ion trap mass spectrometry and quantified using an internal standard, 2 deoxy-glucose 6-phosphate. The kinetic parameters, K(M) and V(max) for the two substrates were determined without using a coupling enzyme as is normally employed in the traditional spectrophotometric assay for systems lacking a chromophore. In addition, hexokinase was successfully immobilized onto an amino-link gel, and a mock library was screened against the immobilized enzyme for the identification of possible inhibitors. After comparing the mass spectra of the library before and after incubation, trehalose 6-phosphate, ADP, and oxidized glutathione were differentiated from other weak or non-inhibitors. Inhibition behavior of ADP with respect to ATP was further evaluated with the ESI-MS assay and the value of K(i) was determined. This ESI-MS assay was demonstrated to be both accurate and precise for determining kinetic constants and for identifying enzyme inhibitors. 相似文献
100.