全文获取类型
收费全文 | 245962篇 |
免费 | 1491篇 |
国内免费 | 422篇 |
专业分类
化学 | 113045篇 |
晶体学 | 3822篇 |
力学 | 13008篇 |
综合类 | 3篇 |
数学 | 38106篇 |
物理学 | 79891篇 |
出版年
2021年 | 1026篇 |
2020年 | 1191篇 |
2019年 | 1257篇 |
2018年 | 10473篇 |
2017年 | 11334篇 |
2016年 | 6608篇 |
2015年 | 2426篇 |
2014年 | 2487篇 |
2013年 | 6174篇 |
2012年 | 9172篇 |
2011年 | 18507篇 |
2010年 | 11373篇 |
2009年 | 11443篇 |
2008年 | 16271篇 |
2007年 | 19712篇 |
2006年 | 5608篇 |
2005年 | 11768篇 |
2004年 | 7955篇 |
2003年 | 7564篇 |
2002年 | 5467篇 |
2001年 | 5729篇 |
2000年 | 4295篇 |
1999年 | 3133篇 |
1998年 | 2173篇 |
1997年 | 2240篇 |
1996年 | 2261篇 |
1995年 | 2033篇 |
1994年 | 2016篇 |
1993年 | 1816篇 |
1992年 | 2292篇 |
1991年 | 2380篇 |
1990年 | 2217篇 |
1989年 | 2190篇 |
1988年 | 2177篇 |
1987年 | 2184篇 |
1986年 | 1991篇 |
1985年 | 2473篇 |
1984年 | 2504篇 |
1983年 | 2010篇 |
1982年 | 2016篇 |
1981年 | 1862篇 |
1980年 | 1843篇 |
1979年 | 2140篇 |
1978年 | 2231篇 |
1977年 | 2082篇 |
1976年 | 2050篇 |
1975年 | 1921篇 |
1974年 | 1904篇 |
1973年 | 1977篇 |
1972年 | 1274篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
181.
The buffer extracts (3S) of sclerotia of Sclerotinia sclerotiorum IFO 9395 contained mitogenic substance(s) to murine splenocytes (Shinohara et al. Chem. Pharm. Bull., 38, 2219 (1990)). Although the native 3S was slightly mitogenic, heating of 3S induced significant mitogenic activity. To isolate the mitogen, we separated 3S by ion-exchange and gel filtration chromatographies. The isolated mitogen, named sclerogen, has a molecular mass of 32 kilodaltons (kDa) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and the isoelectric point (pI) of 5.9 by chromatofocusing. Sclerogen was significantly mitogenic in vitro against murine splenocytes after heat denaturation, and also showed the augmentation of the primary mixed lymphocyte reaction (MLR) in vitro. However, sclerogen did not show the activation of an alternative pathway of complement and hemagglutination activity. These results suggest that sclerogen is a unique mitogen which differs from lectins and shows mitogenicity after heat denaturation. 相似文献
182.
The presence of copper atoms as continuous networks at the grain boundaries of an aluminium-copper alloy has been considered not preventing the moving of dislocations during creep (or at least partially). The dislocations can bs absorbed by these boundaries and penetrate through them. That leads to changés of shape and structure of grains and also to the sliding of grains against each other. This was deduced from the accelerating increase in the sensitivity of the steady state creep rate to the applied stress of an aluminium 2·8 wt% copper alloy examined at wide range of temperatures (50–350 °C) and applied stresses (7–170 MPa). This rapid increase in the sensitivity parameter of the steady state creep rate occurs in Al-Cu alloys at quite higher ranges of applied stresses and may be attributed mainly to the contribution of the grain boundary movements to the creep strain. 相似文献
183.
Robert M. O'Keefe 《The Journal of the Operational Research Society》1989,40(5):415-422
Cognitive style refers to differences that can be perceived in individuals due to differing cognitive structures. There has been a large amount of research on how cognitive style affects managerial decision-making, particularly in the context of management information systems, but little or no attempt to relate these findings to operational research. This paper reviews the findings of cognitive-style research from the perspective of operational research, and draws a number of useful inferences concerning the matching of OR aids to managers, the presentation of information and recommendations, the use and acceptance of OR, and the structure of OR groups. Further, it is argued that cognitive-style findings help to give a justification to the move towards ‘soft’ approaches to analysis. 相似文献
184.
185.
William F. Bowlin 《The Journal of the Operational Research Society》1987,38(2):127-135
The objective of this research is to evaluate a new methodology, data envelopment analysis (DEA), as a tool for measuring and evaluating the operational efficiency of US Air Force organizations. This study involves the application of DEA to locate possible inefficiencies in the performance of US Air Force real-property maintenance activities. Dynamic behaviour, as exhibited via window analyses, is reviewed along with static counterparts. The testing was done in close coordination with Air Force officials, who reviewed the results for accuracy, validity and relevance. We conclude that this type of efficiency analysis does have value for the Air Force, where it can serve as a guide to auditors, budget programmers, managers and others in measuring, evaluating and enhancing operational efficiency. 相似文献
186.
We study matter-wave solitons in Bose-Einstein condensates of ultracold gaseous atoms with spin degrees of freedom and present a class of exact solutions based on the inverse scattering method. The one-soliton solutions are classified with respect to the spin states. We analyze collisional effects between solitons in the same or different spin state(s), which reveals a very interesting possibility: we can manipulate the spin dynamics by controlling the parameters of colliding solitons. 相似文献
187.
188.
The occurrence and formation of black spots areas in PolyLED devices has been studied by time-of-flight SIMS (TOFSIMS). The composition, shape and position of the black spots is visualised by three-dimensional (3D)-TOFSIMS depth-profiling. It has been established that the formation of non-emissive spots is due to the growth of aluminium oxide clusters at the AlBa/polymer interface. Electron injection in the black spots is lost by the resulting local increase of the resistivity of the cathode. 相似文献
189.
Photoisomerization of provitamin D 3 (7-dehydrocholesterol) in a nematic liquid crystal (ZLI-1695, Merck) is investigated in detail by UV absorption spectroscopy. It is found that dissolution of chiral molecules of provitamin D 3 induces the cholesteric phase in a nematic. The spectral kinetics of photoisomerization in this phase changes significantly from that in an ethanol solution. A sharp nonmonotonic dependence of the increase in accumulation of trans isomer tachysterol in a liquid crystal matrix with a decrease in the induced cholesteric pitch from 2200 to 25 μm is revealed. 相似文献
190.
Yu. V. Vasil’ev R. R. Abzalimov Sh. K. Nasibullaev R. F. Tuktarov F. Hauke U. Reuther A. Hirsch T. Drewello 《Physics of the Solid State》2002,44(3):554-556
The formation and decay of negative molecular ions of azafullerenes and their hydrogenated derivatives are investigated by mass spectrometry. The mechanisms of resonant electron capture and the lifetimes of negative molecular ions with respect to the electron autodetachment in azafullerene molecules are discussed. A comparative analysis of the data obtained for azafullerenes and hydrogenated fullerene derivatives is carried out. 相似文献