全文获取类型
收费全文 | 21726篇 |
免费 | 378篇 |
国内免费 | 301篇 |
专业分类
化学 | 11778篇 |
晶体学 | 197篇 |
力学 | 1534篇 |
综合类 | 17篇 |
数学 | 3400篇 |
物理学 | 5479篇 |
出版年
2020年 | 294篇 |
2019年 | 373篇 |
2018年 | 482篇 |
2017年 | 458篇 |
2016年 | 606篇 |
2015年 | 342篇 |
2014年 | 546篇 |
2013年 | 934篇 |
2012年 | 716篇 |
2011年 | 765篇 |
2010年 | 734篇 |
2009年 | 690篇 |
2008年 | 719篇 |
2007年 | 720篇 |
2006年 | 555篇 |
2005年 | 506篇 |
2004年 | 471篇 |
2003年 | 494篇 |
2002年 | 531篇 |
2001年 | 481篇 |
2000年 | 363篇 |
1999年 | 287篇 |
1998年 | 254篇 |
1997年 | 245篇 |
1996年 | 242篇 |
1993年 | 242篇 |
1992年 | 245篇 |
1991年 | 251篇 |
1990年 | 275篇 |
1989年 | 269篇 |
1987年 | 245篇 |
1985年 | 288篇 |
1984年 | 294篇 |
1983年 | 269篇 |
1982年 | 286篇 |
1981年 | 259篇 |
1980年 | 265篇 |
1979年 | 312篇 |
1978年 | 334篇 |
1977年 | 329篇 |
1976年 | 415篇 |
1975年 | 367篇 |
1974年 | 397篇 |
1973年 | 407篇 |
1972年 | 374篇 |
1971年 | 332篇 |
1970年 | 316篇 |
1969年 | 302篇 |
1968年 | 262篇 |
1967年 | 251篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
V. O. Kur'yanov T. F. Zhelobetskaya A. E. Zemlyakov V. Ya. Chirva 《Chemistry of Natural Compounds》1993,29(1):103-106
The synthesis has been effected of derivatives of MDP having a spacer with an amino or carboxy group. The final stage of the synthesis was the condensation of Boc-L-Ala-D-iGln with 6-aminohexanol (followed by the two-stage replacement of the hydroxy by an azido group) or with benzyl 6-aminohexanoate.Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 122–125, January–February, 1993. 相似文献
43.
S. Ya. Yakubov 《Results in Mathematics》1995,28(1-2):153-168
In this paper we find conditions guarantee that irregular boundary value problems for elliptic differential-operator equations of the second order in an interval are fredholm. We apply this result to find some algebraic conditions guarantee that irregular boundary value problems for elliptic partial differential equations of the second order in cylindrical domains are fredholm. Apparently this is the first paper where the regularity of an elliptic boundary value problem is not satisfied on a manifold of the dimension equal to dimension of the boundary. Nevertheless the problem is fredholm and the resolvent is compact. It is interesting to note that the considered boundary value problems for elliptic equations in a cylinder being with separating variables are noncoercive. 相似文献
44.
The NH,NH-dihydrocycloadduct 1 (6-chloro-9,9-dimethyl-7,8-dihydro-9H-pyrazolo[4,3-d]tetrazolo[1,5-b]-pyridazine) obtained by the cycloaddition of 2-diazopropane to 6-chlorotetrazolo[1,5-b]pyridazine, is transformed with protected or unprotected carbohydrates 2, 5, 7,9, 11, 13 and 15 in the presence of methyl acrylate ( 3 ) into the corresponding C-nucleosides 4,6,8,10,12,14 and 16 . In this one-pot synthesis two new chiral centers are formed stereoselectively, dependent on the chirality at C-atom next to aldehydo group in the carbohydrate. 相似文献
45.
E. Ya. Paryev 《Physics of Atomic Nuclei》2006,69(2):332-354
Within the spectral function approach, we study the direct production and decay via the dikaon (dimuon) channel of ϕ mesons
in the interactions of 2.4-and 2.7-GeV protons with light and medium target nuclei. It is shown that the K
+
K
− (μ+ μ−) invariant-mass distribution consists of the two components, which correspond to the ϕ decay “outside” and “inside” the target nucleus. The first (narrow) component has the free ϕ width, while the second (broad) component is distorted by the nuclear matter owing to resonance-nucleon scattering and a
possible in-medium modification of the kaons and ρ meson at finite baryon density. The relative strength of the “inside” and “outside” components is analyzed in different scenarios
for the ϕ width and momentum cut. It is demonstrated that the width of the resulting dimuon invariant-mass distribution on medium nuclei
is larger than the free ϕ width by a factor of about 2 if the total ϕ in-medium width is used and the respective cutoff for the ϕ three-momentum is applied, whereas the resulting dikaon invariant-mass distribution has an insignificant sensitivity to the
ϕ in-medium properties owing to the strong absorption of the K
− in the surrounding nuclear matter. On the other hand, because of the distortion of the K
+ and K
− on their way out of the target nucleus mainly due to the hadronic kaon potentials, the latter distribution is broadened and
shifted to higher invariant masses, which means that the measurement of such broadening would give additional evidence for
the modification of the kaon and antikaon properties in the nuclear medium.
The text was submitted by the author in English. 相似文献
46.
Mustafa Çelebier Ertan Şahin Nilgün Ancın Nurşen Altuntaş Öztaş Selma Gül Öztaş 《应用有机金属化学》2007,21(10):viii-viii
The article referenced above was first published online on 30 August 2007 with incorrect pagination; the pagination has now been corrected online and in print. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
47.
48.
S. V. Valueva L. N. Borovikova V. V. Koreneva Ya. I. Nazarkina A. I. Kipper V. V. Kopeikin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(7):1170-1173
Nanostructures formed during the reduction of ionic selenium in the selenite-ascorbate redox system in an aqueous solution of bovine serum albumin (BSA) were studied using static and dynamic light scattering and flow birefringence. It was established that this process results in the formation of stable aggregates of selenium nanoparticles that adsorb BSA molecules. It was found that highly-ordered superhigh-molecular-weight spherical nanostructures with high density and unique morphology are formed. Experiments with a cell culture of promyelocytic leukemia HL-60 showed that BSA adsorbed on selenium nanoparticles can inhibit the growth of tumor cells and deactivate free radicals with an efficiency comparable with that of sodium selenite. 相似文献
49.
The theory of dielectric space-charge polarization losses describes well both the model of an inhomogeneous dielectric [1]
and the polarization resulting from mosaic blocks of alkali-halide crystals [2]. The Debye frequency dependences ε*(ω) and
tan δ(ω) with non-Arrhenius relaxation time are calculated in the first approximation of perturbation theory [3, 4] with the
use of a nonlinear system of the Fokker-Planck and Poisson equations for the interlayer polarization with allowance for tunnel
transitions of relaxation oscillators. For the Maxwell mechanism of space-charge relaxation, tan δ(ω) also has the Debye form
[5]. It should be noted that in studies cited above the electric field was considered uniform, and the nonlinearity of the
initial system of equations was not investigated. This paper removes these restrictions and elaborates a theory of relaxation
mechanism.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 28–34, November, 2006. 相似文献
50.
The exact solution is constructed to a torsion problem for a circular elastic shaft in a medium referred to a spherical coordinate system. One end of the shaft is rigidly fixed and the other is subjected to either tangential forces or a torque. New integral transforms are obtained to solve the problem. 相似文献