全文获取类型
收费全文 | 542509篇 |
免费 | 7590篇 |
国内免费 | 3314篇 |
专业分类
化学 | 279625篇 |
晶体学 | 7848篇 |
力学 | 26925篇 |
综合类 | 147篇 |
数学 | 69350篇 |
物理学 | 169518篇 |
出版年
2021年 | 5611篇 |
2020年 | 6192篇 |
2019年 | 6952篇 |
2018年 | 9030篇 |
2017年 | 9151篇 |
2016年 | 12430篇 |
2015年 | 7022篇 |
2014年 | 11385篇 |
2013年 | 24681篇 |
2012年 | 19793篇 |
2011年 | 23216篇 |
2010年 | 17383篇 |
2009年 | 17336篇 |
2008年 | 21756篇 |
2007年 | 21423篇 |
2006年 | 19467篇 |
2005年 | 17333篇 |
2004年 | 15994篇 |
2003年 | 14344篇 |
2002年 | 14201篇 |
2001年 | 15020篇 |
2000年 | 11584篇 |
1999年 | 8997篇 |
1998年 | 7793篇 |
1997年 | 7658篇 |
1996年 | 7086篇 |
1995年 | 6406篇 |
1994年 | 6374篇 |
1993年 | 6134篇 |
1992年 | 6469篇 |
1991年 | 6947篇 |
1990年 | 6639篇 |
1989年 | 6527篇 |
1988年 | 6363篇 |
1987年 | 6164篇 |
1986年 | 5899篇 |
1985年 | 7436篇 |
1984年 | 7783篇 |
1983年 | 6552篇 |
1982年 | 6822篇 |
1981年 | 6334篇 |
1980年 | 6009篇 |
1979年 | 6512篇 |
1978年 | 6742篇 |
1977年 | 6633篇 |
1976年 | 6587篇 |
1975年 | 6305篇 |
1974年 | 6132篇 |
1973年 | 6425篇 |
1972年 | 4707篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
温度对PSⅡCP4 7/D1/D2/Cytb559复合物荧光光谱特性的影响 总被引:3,自引:3,他引:0
采用激励光源为514.5 nm的分幅扫描单光子计数荧光光谱装置对经20℃、42℃和48℃不同温度处理后的反应中心复合物CP47/D1/D2/Cyt b559的荧光光谱特性进行了研究.经解析,获得不同温度处理后,CP47/D1/D2/Cyt b559复合物最大峰值未发生变化,均在682 nm,说明Chla670的能量都由Chla682接收,但损耗愈来愈小,在48℃时,损耗程度最小,而其荧光百分比未发生多大变化.振动副带~700 nm和~740 nm的中心波长都发生蓝移,在不同温度下分别为:20℃ 703 nm,749 nm;42℃ 697 nm,744 nm;48℃ 694 nm,740 nm.因此可以推测温度的升高,影响了CP47/D1/D2/Cyt b559色素蛋白的二级结构以及色素分子的空间位置,使最大峰值处的荧光强度逐渐降低,振动副带逐渐蓝移.42℃的温度已造成影响,48℃影响较大. 相似文献
992.
The method of nonlinear moments, when used to solve the Boltzmann equation, necessitates the calculation of collision integral
matrix elements. The matrix elements are hard to calculate numerically, especially at large indices. The asymptotics of the
matrix elements are constructed. In terms of the model of pseudopower particle interaction, a formula free of summation is
derived. This makes it possible to find the asymptotic behavior of linear and nonlinear elements when two indices are large.
For an arbitrary interaction cross section, asymptotic expansions of linear and nonlinear matrix elements in one index are
obtained. For Maxwellian molecules, asymptotic formulas are derived for three large indices. 相似文献
993.
O. V. Sizova E. P. Sokolova V. I. Baranovskii D. A. Rozmanov O. A. Tomashenko 《Journal of Structural Chemistry》2004,45(5):762-770
Ab initio MP2 calculations with several basis sets proved the existence of a stable benzonitrile dimer with a planar structure and a short contact between the H atom of one molecule and the N atom of another. The structure is greatly stabilized by attraction between the neighboring oppositely directed dipoles and donor-acceptor interaction between the orbital of the lone electron pair of the N′ atom and the vacant antibonding orbital localized on the C-H bond.Original Russian Text Copyright © 2004 by O. V. Sizova, E. P. Sokolova, V. I. Baranovskii, D. A. Rozmanov, and O. A. Tomashenko__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 807–815, September–October, 2004. 相似文献
994.
The effect of bacterial and fungal activities on organic matter degradation in Brazilian soils was studied by a microcalorimetric method. Bacteria and fungi isolated from tropical soils and added to: Rhodic eutrudox (R), Typic eutrudox (V) and Quartzipsamment (Q) soils amended separately with moisture (control) (A) and 25% of cattle manure (E), municipal refuse compost (L), earthworm casts (H) or 23 μg of trifluralin (T) were investigated. The number of colony forming units in soil suspension was quantified by microscopy and inoculated in respective soil. All processes were measured at intervals of 7 days over a period of 35 days. The exothermic thermal effect (μJ) per cm3 of bacteria or fungi per gram of dry soil, respectively, for each substrate was: [(9±1), (4±1)] RA; [(478±24), (105±5)] RE; [(121±6), (71±4)] RL; [(121±6), (71±4)] RH; [(8±1); (3±1)] RT; [(10±1), (9±1] VA; [(347±17), (261±13)] VE; [(71±4), (28±1)] VL; [(22±1), (33±2)] VH; [(7±1), (10±1)] VT; [(19±1), (12±1)] QA; [(1301±65), (46±2)] QE; [(89±4), (9±1)] QL; [(130±7), (11±1)] QH; [(32±2), (8±1)] QT. The calorimetric values are higher for bacteria than for fungi. In general, the results showed higher activities in the soil amended with cattle manure than with other additives. 相似文献
995.
H. H. Salah M. Darwish A.-S. F. Obada 《International Journal of Theoretical Physics》2003,42(3):549-567
The odd excited negative binomial states are introduced using the photon creation operator by repeated application on negative binomialstates. These states interpolate between the odd displaced Fock states and the odd excited pure thermal states. In this paper both squeezing phenomena (normal squeezing and amplitude squared squeezing) are discussed. Besides discussion of the Glauber second-order correlation function, investigations are carried out for the quasi-probability distribution functions (Wigner function and Q-function). Finally the Pegg-Barnett phase probability distribution is computed for these states. 相似文献
996.
Relationships between the electrodynamic (wave propagation constants) and quantum-mechanical parameters (probability of induced transitions) of interaction between energy quanta and particles of the medium are derived for dipole and paramagnetic interaction types. It is demonstrated that quantum-mechanical parameters are generally complex. 相似文献
997.
We prove that any irreducible faithful representation of an almost torsion-free Abelian group G of finite rank over a finitely generated field of characteristic zero is induced from an irreducible representation of a finitely generated subgroup of the group G. 相似文献
998.
We establish the existence of a weak solution to the Dirichlet problem belonging to a Sobolev space for nonlinear elliptic equations of second order with right-hand sides from a wide class of functions defined in terms of the logarithmic function. 相似文献
999.
The fine-structure parameters of a series of configurations of the first ion of indium and the gyromagnetic ratios in intermediate coupling are calculated by a semiempirical method in the single-configuration approximation. 相似文献
1000.