全文获取类型
收费全文 | 146575篇 |
免费 | 7185篇 |
国内免费 | 13688篇 |
专业分类
化学 | 87041篇 |
晶体学 | 2421篇 |
力学 | 3544篇 |
综合类 | 969篇 |
数学 | 41301篇 |
物理学 | 32172篇 |
出版年
2023年 | 934篇 |
2022年 | 2334篇 |
2021年 | 2210篇 |
2020年 | 2741篇 |
2019年 | 3536篇 |
2018年 | 3142篇 |
2017年 | 3641篇 |
2016年 | 3645篇 |
2015年 | 3326篇 |
2014年 | 4904篇 |
2013年 | 10115篇 |
2012年 | 7972篇 |
2011年 | 8423篇 |
2010年 | 7198篇 |
2009年 | 8826篇 |
2008年 | 9470篇 |
2007年 | 9801篇 |
2006年 | 8640篇 |
2005年 | 7040篇 |
2004年 | 6935篇 |
2003年 | 5926篇 |
2002年 | 7325篇 |
2001年 | 4724篇 |
2000年 | 4375篇 |
1999年 | 4253篇 |
1998年 | 3746篇 |
1997年 | 2884篇 |
1996年 | 2415篇 |
1995年 | 2255篇 |
1994年 | 2053篇 |
1993年 | 1673篇 |
1992年 | 1571篇 |
1991年 | 1047篇 |
1990年 | 867篇 |
1989年 | 824篇 |
1988年 | 611篇 |
1987年 | 521篇 |
1986年 | 473篇 |
1985年 | 614篇 |
1984年 | 547篇 |
1983年 | 339篇 |
1982年 | 464篇 |
1981年 | 536篇 |
1980年 | 499篇 |
1979年 | 342篇 |
1978年 | 387篇 |
1977年 | 318篇 |
1976年 | 277篇 |
1975年 | 153篇 |
1974年 | 163篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
阐述检测物体是否产生了电场的方法;通过实际检测证实立方体永磁体既产生了负静电场,也产生了正静电场,并测定了具体的场强. 相似文献
132.
meso-Tetra(n-hexyloxycarbonyl)porphyrin was found to be converted into porphine, the mother compound of porphyrins, in a 77% yield when heated in aqueous sulfuric acid at 180 °C over 30 min under an inert atmosphere. The observation demonstrates that the substituted porphyrin serves as a novel and useful precursor for porphine. 相似文献
133.
Wu Hongyi 《高校应用数学学报(英文版)》2006,21(1):96-106
A family of Said-Bézier type generalized Ball (SBGB) bases and surfaces with a parameter H over triangular domain is introduced, which unifies Bézier surface and Said-Ball surface and includes several intermediate
surfaces. To convert different bases and surfaces, the dual functionals of bases are presented. As an application of dual
functionals, the subdivision formulas for surfaces are established. 相似文献
134.
S. Meenakshi B.K. Godwal I. Orgzall S. Tkachev 《Journal of Physics and Chemistry of Solids》2006,67(8):1660-1667
We report the results of an X-ray diffraction study of CdAl2Se4 and of Raman studies of HgAl2Se4 and ZnAl2Se4 at room temperature, and of CdAl2S4 and CdAl2Se4 at 80 K at high pressure. The ambient pressure phase of CdAl2Se4 is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A fit of the volume pressure data to a Birch-Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at ∼9 GPa is about 10%. The analysis of the Raman data of HgAl2Se4 and ZnAl2Se4 reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order-disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl2S4 and CdAl2Se4, which shows a very weak temperature dependence of the Raman-active phonon modes. 相似文献
135.
Dual fractional cutting plane algorithms, in which cutting planes are used to iteratively tighten a linear relaxation of an integer program,
are well-known and form the basis of the highly successful branch-and-cut method. It is rather less well-known that various primal cutting plane algorithms were developed in the 1960s, for example by Young. In a primal algorithm, the main role of the cutting
planes is to enable a feasible solution to the original problem to be improved. Research on these algorithms has been almost
non-existent.
In this paper we argue for a re-examination of these primal methods. We describe a new primal algorithm for pure 0-1 problems based on strong valid inequalities and give some encouraging computational results. Possible extensions to the case of general
mixed-integer programs are also discussed. 相似文献
136.
137.
138.
We obtain upper bounds for the tail distribution of the first nonnegative sum of a random walk and for the moments of the overshoot over an arbitrary nonnegative level if the expectation of jumps is positive and close to zero. In addition, we find an estimate for the expectation of the first ladder epoch. 相似文献
139.
140.
Kasper K. Berthelsen Jesper Møller 《Bulletin of the Brazilian Mathematical Society》2002,33(3):351-367
This primer provides a self-contained exposition of the case where spatial birth-and-death processes are used for perfect
simulation of locally stable point processes. Particularly, a simple dominating coupling from the past (CFTP) algorithm and
the CFTP algorithms introduced in [13], [14], and [5] are studied. Some empirical results for the algorithms are discussed.
Received: 30 June 2002 相似文献