全文获取类型
收费全文 | 15406篇 |
免费 | 2023篇 |
国内免费 | 2034篇 |
专业分类
化学 | 14708篇 |
晶体学 | 202篇 |
力学 | 483篇 |
综合类 | 74篇 |
数学 | 157篇 |
物理学 | 3839篇 |
出版年
2024年 | 49篇 |
2023年 | 210篇 |
2022年 | 481篇 |
2021年 | 701篇 |
2020年 | 1018篇 |
2019年 | 745篇 |
2018年 | 512篇 |
2017年 | 525篇 |
2016年 | 677篇 |
2015年 | 713篇 |
2014年 | 780篇 |
2013年 | 1180篇 |
2012年 | 999篇 |
2011年 | 817篇 |
2010年 | 617篇 |
2009年 | 791篇 |
2008年 | 827篇 |
2007年 | 930篇 |
2006年 | 821篇 |
2005年 | 706篇 |
2004年 | 666篇 |
2003年 | 630篇 |
2002年 | 596篇 |
2001年 | 426篇 |
2000年 | 388篇 |
1999年 | 335篇 |
1998年 | 330篇 |
1997年 | 233篇 |
1996年 | 236篇 |
1995年 | 238篇 |
1994年 | 183篇 |
1993年 | 179篇 |
1992年 | 158篇 |
1991年 | 109篇 |
1990年 | 91篇 |
1989年 | 73篇 |
1988年 | 69篇 |
1987年 | 66篇 |
1986年 | 48篇 |
1985年 | 47篇 |
1984年 | 39篇 |
1983年 | 18篇 |
1982年 | 28篇 |
1981年 | 24篇 |
1980年 | 35篇 |
1979年 | 30篇 |
1978年 | 19篇 |
1977年 | 17篇 |
1976年 | 17篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
养殖池塘沉积物的重金属分布及污染特征 总被引:3,自引:0,他引:3
浙江省淅西北地区淡水养殖池塘沉积物重金属调查研究表明,养殖池塘沉积物中7种重金属元素分布不均衡,差异也较大,除Hg和Cr元素外,其余重金属元素已大大超过土壤本底值.虽然其实测含量都未超出国家规定的标准值范围,但沉积物中重金属元素对养殖水环境、养殖品种存在的潜在污染与危害值得关注.污染指数评价显示,养殖池塘沉积物中主要污染物质为Cu和Cr,而Hg、Pb污染程度相对较轻. 相似文献
42.
I. Iovel L. Golomba J. Popelis S. Grinberga E. Lukevics 《Chemistry of Heterocyclic Compounds》2003,39(1):49-55
The addition of hydrosilanes (HSiEt3, HSiMe2Ph, H2SiPh2) to the CH=N bond of heterocyclic azomethines has been studied in the presence of monovalent complexes of rhodium and palladium. The effect on the reaction of the CF3 group of the aldimines, which were obtained from O-, S-, and N-heteroaromatic aldehydes and 2-trifluoromethylaniline, has been clarified, as were other regularities of the processes being studied. A series of corresponding furans, thiophenes, and pyridine amines has been synthesized. 相似文献
43.
44.
The Monte Carlo ray-tracing method (MCRT) based on the concept of radiation distribution factor is extended to solve radiative heat transfer problem in turbulent fluctuating media under the optically thin fluctuation approximation. A one-dimensional non-scattering turbulent fluctuating media is considered, in which the mean temperature and absorption coefficient distribution are assumed and the shape of probability density function is given. The distribution of the time-averaged volume radiation heat source is solved by MCRT and direct integration method. It is shown that the results of MCRT based on the concept of radiation distribution factor agree with these of integration solution very well, but results of MCRT based on the concept of radiative transfer coefficient do not agree with these of integration solution. The solution of time-averaged radiative transfer equation by the concept of radiative transfer coefficient should be treated with caution. 相似文献
45.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
46.
Maria G. Semenova Larisa E. Belyakova Anna S. Antipova Yu. N. Polikarpov Lida Klouda Anna Markovic Michael M. Il'in 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):47-54
We report on the effect of commercially important polysaccharides (maltodextrins with variable dextrose equivalent (Paselli SA-2, MD-6 and MD-10) on the surface activity at the air–water interface of small-molecule surfactants (sms), possessing different hydrophobic–lipophilic balance ((SSL (Na+), the main component is a sodium salt of stearol–lactoyl lactic acid, and PGE (080), polyglycerol ester of C18 fatty acid), and widely used in food products. A marked change of the surface activity of sms was found in the presence of maltodextrins by tensiometry. The combined data of laser multiangle light scattering and mixing calorimetry have suggested that this result is governed by specific complex formation between maltodextrins and sms in aqueous medium. Measurements have been made of the molar mass, the second virial coefficient and the enthalpy of intermolecular interactions in aqueous solutions. The implication of a degree of polymerization of maltodextrins in this phenomenon was shown. The interrelation between the molecular parameters of the formed complexes and their surface activity at the air–water interface has been revealed and discussed. 相似文献
47.
In the present paper, a new two-parameter inverted equation of state (EOS) is developed which is found to be working very
well in the high-pressure region. To check its success and validity, this EOS has been applied in a number of solids. The
computed volume compression is found to be in very good agreement with the experimental data in the whole range of pressure
in all the solids. The minimum and the maximum pressure range used in the present study is 0–320 kbar and 0–3000 kbar, respectively. 相似文献
48.
A. D. Krisch 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):417-423
There will be a review of the history of polarized proton beams, and a discussion of the unexpected and still unexplained
large transverse spin effects found in several high-energy proton-proton spin experiments at the ZGS, AGS and Fermilab. Next,
there will be a discussion of present and possible future experiments on the violent elastic collisions of polarized protons
at IHEP-Protvino's 70GeV U-70 accelerator in Russia and the new high-intensity 50GeV J-PARC facility being built at Tokai
in Japan. 相似文献
49.
50.
We considered the kaon absorption from atomic states into the nucleus. We found that the nuclear density probed by the atomic
kaon significantly depends on the kaon orbit. Then, we re-examined the meanings of the observed strengths of one-body and
two-body kaon absorption, and investigated the effects to the formation spectra of kaon bound states by in-flight (K
-, p) reactions. As a natural consequence, if the atomic kaon probes a smaller nuclear density, the ratio of the two-body absorption
at nuclear center is larger than the observed value in kaonic atoms, and the depth of the imaginary potential is deeper even
at smaller kaon energies as in kaonic nuclear states because of the large phase space for the two-body processes. This deeper
imaginary potential makes the signals of kaonic nucleus formation more unclear in the (K
-, p) spectra. 相似文献