全文获取类型
收费全文 | 551393篇 |
免费 | 7253篇 |
国内免费 | 1840篇 |
专业分类
化学 | 296839篇 |
晶体学 | 8038篇 |
力学 | 24485篇 |
综合类 | 18篇 |
数学 | 64536篇 |
物理学 | 166570篇 |
出版年
2021年 | 4424篇 |
2020年 | 4950篇 |
2019年 | 5326篇 |
2018年 | 6654篇 |
2017年 | 6536篇 |
2016年 | 10382篇 |
2015年 | 6885篇 |
2014年 | 10226篇 |
2013年 | 25636篇 |
2012年 | 19783篇 |
2011年 | 24509篇 |
2010年 | 16727篇 |
2009年 | 16691篇 |
2008年 | 22312篇 |
2007年 | 22287篇 |
2006年 | 20821篇 |
2005年 | 18832篇 |
2004年 | 17350篇 |
2003年 | 15258篇 |
2002年 | 15010篇 |
2001年 | 16941篇 |
2000年 | 12829篇 |
1999年 | 10092篇 |
1998年 | 8241篇 |
1997年 | 8009篇 |
1996年 | 7818篇 |
1995年 | 7005篇 |
1994年 | 6800篇 |
1993年 | 6557篇 |
1992年 | 7370篇 |
1991年 | 7447篇 |
1990年 | 7066篇 |
1989年 | 6855篇 |
1988年 | 6875篇 |
1987年 | 6724篇 |
1986年 | 6392篇 |
1985年 | 8493篇 |
1984年 | 8647篇 |
1983年 | 6905篇 |
1982年 | 7147篇 |
1981年 | 7039篇 |
1980年 | 6597篇 |
1979年 | 6995篇 |
1978年 | 7181篇 |
1977年 | 7042篇 |
1976年 | 6972篇 |
1975年 | 6578篇 |
1974年 | 6483篇 |
1973年 | 6532篇 |
1972年 | 4419篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
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
912.
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
913.
Previous studies of the initial stage of oxidation on clean single crystal of Cu(1 0 0) have been extended to the case of the Cu(1 1 0) surface. The dynamic observation of the nucleation and growth of Cu oxide by means of in situ ultra high vacuum transmission electron microscopy (UHV-TEM) shows a highly enhanced oxidation rate on Cu(1 1 0) surface as compared to Cu(1 0 0). The kinetic data on the nucleation and growth of the three-dimensional oxide islands agree well with our heteroepitaxial model of surface diffusion of oxygen. 相似文献
914.
Chemisorption at interfaces between organic semiconductors and metals: role of the electron affinity
Chemisorption is a well-known phenomenon for many interfaces between organic semiconductors and metals. It is shown that many published data indicate that the occurrence of chemisorption can be rationalized upon the consideration of the metal work function versus the electron affinity of the organic semiconductor. 相似文献
915.
Zavarzin I. V. Smirnova N. G. Chernoburova E. I. Yarovenko V. N. Krayushkin M. M. 《Russian Chemical Bulletin》2004,53(6):1257-1260
A method for syntheses of previously unknown derivatives of thieno[2,3-d]pyrimidines and quinazolines from monothiooxamides was proposed. 相似文献
916.
Hyperfine Interactions - Corrosion products formed on low alloy steel under two marine environments are characterised. Both environments are classified as C4 according to the ISO 9223 Standard. The... 相似文献
917.
The concept of the Moore-Penrose inverse in an indefinite inner product space is introduced. Extensions of some of the formulae in the Euclidean space to an indefinite inner product space are studied. In particular range-hermitianness in completely characterized. Equivalence of a weighted generalized inverse and the Moore-Penrose inverse is proved. Finally, methods of computing the Moore-Penrose inverse are presented. 相似文献
918.
为阐述放射性9C束流应用于治癌的物理基础, 运用一个球形生物组织等效正比计数器测量了9C束流不同贯穿深度上的线能谱, 得到了沿束流贯穿深度上的剂量平均线能分布. 将实验测量得到的线能谱转换成为不同传能线密度在吸收剂量中所占份额的分布, 得到了该9C束流在不同贯穿深度上的剂量平均传能线密度分布. 将生物组织等效正比计数器测量得到的与先前通过平行板正比计数器测量得到的该9C束流的剂量平均传能线密度分布进行比较, 发现: 在束流入射通道上, 两者测量数据符合很好, 而在束流Bragg峰附近9C离子的沉积区域, 由组织等效正比计数器测量得到的剂量平均传能线密度值大于由平行板正比计数器测量得到的值. 相似文献
919.
M. A. Bertolim M. P. Mello K. A. de Rezende 《Transactions of the American Mathematical Society》2005,357(10):4091-4129
In this article the main theorem establishes the necessity and sufficiency of the Poincaré-Hopf inequalities in order for the Morse inequalities to hold. The convex hull of the collection of all Betti number vectors which satisfy the Morse inequalities for a pre-assigned index data determines a Morse polytope defined on the nonnegative orthant. Using results from network flow theory, a scheme is provided for constructing all possible Betti number vectors which satisfy the Morse inequalities for a pre-assigned index data. Geometrical properties of this polytope are described.
920.
Timothy M. Chan 《Discrete and Computational Geometry》2005,34(1):11-24
We give a surprisingly short proof that in any planar arrangement of n curves where each pair intersects at most a fixed number (s) of
times, the k-level has subquadratic (O(n2-1/2s) complexity. This answers one of the main open problems from the author’s previous paper [DCG 29, 375-393 (2003)],
which provided a weaker upper bound for a
restricted class of curves only (graphs of degree-s polynomials).
When combined with existing tools (cutting curves, sampling, etc.),
the new idea generates a slew of improved k-level results for
most of the curve families studied earlier, including a
near-O(n3/2 bound for parabolas. 相似文献