全文获取类型
收费全文 | 2607篇 |
免费 | 23篇 |
国内免费 | 13篇 |
专业分类
化学 | 645篇 |
晶体学 | 4篇 |
力学 | 380篇 |
数学 | 925篇 |
物理学 | 689篇 |
出版年
2023年 | 17篇 |
2022年 | 23篇 |
2021年 | 63篇 |
2020年 | 38篇 |
2019年 | 39篇 |
2018年 | 13篇 |
2017年 | 39篇 |
2016年 | 48篇 |
2015年 | 65篇 |
2014年 | 99篇 |
2013年 | 113篇 |
2012年 | 142篇 |
2011年 | 156篇 |
2010年 | 144篇 |
2009年 | 127篇 |
2008年 | 182篇 |
2007年 | 149篇 |
2006年 | 138篇 |
2005年 | 109篇 |
2004年 | 84篇 |
2003年 | 90篇 |
2002年 | 83篇 |
2001年 | 68篇 |
2000年 | 39篇 |
1999年 | 75篇 |
1998年 | 47篇 |
1997年 | 45篇 |
1996年 | 36篇 |
1995年 | 35篇 |
1994年 | 34篇 |
1993年 | 32篇 |
1992年 | 25篇 |
1991年 | 20篇 |
1990年 | 24篇 |
1989年 | 15篇 |
1988年 | 50篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 10篇 |
1975年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有2643条查询结果,搜索用时 15 毫秒
51.
Summary LetC be the symmetric cusp {(x, y)2:–x
yx
,x0} where >1. In this paper we decide whether or not reflecting Brownian motion inC has a semimartingale representation. Here the reflecting Brownian motion has directions of reflection that make constant angles with the unit inward normals to the boundary. Our results carry through for a wide class of asymmetric cusps too. 相似文献
52.
Tailen Hsing 《Probability Theory and Related Fields》1993,95(3):331-356
Summary Let {
j
} be a stationary sequence of weakly dependent random variables and letM
n
(k)
be thek-th largest value of
j
, 1jn. The estimation of the parameters of the asymptotic distribution ofM
n
(k)
is considered using a procedure motivated by a limit theorem pertaining to the point process
. A number of statistical issues concerning the procedure, including how to select the tuning parameters, are addressed. The second problem that we consider is the estimation of the filter of a moving average process with heavy tails. In particular, the investigation covers the moving average stable process. Motivated by ideas in Rootzén (1978), our estimator uses information contained in the sample behavior of the process near the largest excursion.Research supported by AFOSR Contract No. 91-0030, NAVY-ONR Grant No. N00014-92-J-1007, and NSF Grant No. 9107507 相似文献
53.
Ming Z. Gao 《Tetrahedron letters》2004,45(29):5649-5652
The novel structures of sulfur-containing chiral bis(oxazoline) compounds which have been synthesized have been determined by X-ray crystal diffraction analyses. A high enantioselectivity (ee >99%) in the asymmetric cyclopropanation of diphenylethene with diazoester using the bis(oxazoline)-Ru(II) catalyst was obtained. 相似文献
54.
Piyarat Thanakoses Nagat Abd Alla Mostafa Mark T. Holtzapple 《Applied biochemistry and biotechnology》2003,107(1-3):523-546
Using the MixAlco process, biomass can be converted into carboxylic acids, which can be chemically converted into mixed alcohol
fuels. This study focused on the use of countercurrent fermentation to anaerobically convert sugarcane bagasse and chicken
manure to mixed carboxylic acids using a mixed culture of mesophilic microorganisms from terrestrial and marine sources. Bagasse
was pretreated with lime to increase digestibility. The continuum particle distribution model (CPDM) simulated continuous
fermentors based on data collected from batch experiments. This model saves considerable time in determining optimum operating
conditions. For an 80% bagasse/20% chicken manure fermentation with terrestrial inoculum at a volatile solids loading rate
(VSLR) of 7.36 g/(L of liquid·d) and a liquid residence time (LRT) of 8.88 d, total carboxylic acid productivity, total acid
selectivity, and yield were 2.49 g/(L of liquid·d), 0.581 g of total acid/g of VS digested, and 0.338 g of total acid/g of
VS fed, respectively, at a concentration of 18.7 g of total acid/L. At the same VSLR and LRT, fermentation with marine inoculum
gave higher total acid productivity, total acid selectivity, and yield than fermentation with terrestrial inoculum. For an
80% bagasse/20% chicken manure fermentation with marine inoculum at a VSLR of 3.83 g/(L of liquid·d) and an LRT of 12.1 d,
total carboxylic acid productivity, total acid selectivity, and yield were 1.38 g/(L of liquid·d), 0.667 g of total acid/g
of VS digested, and 0.359 g of total acid/g of VS fed, respectively, at a concentration of 16.2 g of total acid/L. 相似文献
55.
John A. McLean Brandon T. Ruotolo Kent J. Gillig David H. Russell 《International journal of mass spectrometry》2005,240(3):301
Matrix-assisted laser desorption/ionization (MALDI) coupled with ion mobility–mass spectrometry (IM–MS) provides a rapid (μs–ms) means for the two-dimensional (2D) separation of complex biological samples (e.g., peptides, oligonucleotides, glycoconjugates, lipids, etc.), elucidation of solvent-free secondary structural elements (e.g., helices, β-hairpins, random coils, etc.), rapid identification of post-translational modifications (e.g., phosphorylation, glycosylation, etc.) or ligation of small molecules, and simultaneous and comprehensive sequencing information of biopolymers. In IM–MS, protein-identification information is complemented by structural characterization data, which is difficult to obtain using conventional proteomic techniques. New avenues for enhancing the figures of merit (e.g., sensitivity, limits of detection, dynamic range, and analyte selectivity) and optimizing IM–MS experimental parameters are described in the context of deriving new information at the forefront of proteomics research. 相似文献
56.
57.
《Polyhedron》2005,24(16-17):2299-2308
The design and experimental investigations of photo-induced high-spin organic systems (the photo-excited quartet (S = 3/2) and quintet (S = 2) states) is reviewed with focusing π-conjugated organic spin systems. In order to study the photo-induced spin alignments on the excited states, the photo-excited high-spin states of π-conjugated stable radical systems and their π-topological isomers were studied by the time-resolved ESR experiments. The relationship between the π-topology and spin alignment on the photo-excited states is clarified. The mechanism of the photo-induced intramolecular spin alignment and the role of the spin polarization and spin delocalization are revealed with the help of the molecular orbital calculations. One of the key processes for the photo-control of the organic molecular magnetism is established. The guiding principle designing the photo-excited high-spin system and the role of π-topology are clarified. Potential developments toward the functional materials are also proposed utilizing the π-conjugated organic spin systems with the photo-excited high-spin states. 相似文献
58.
Ab initio calculations using the MP2/cc-pVTZ basis set do an excellent job of predicting the inversion barrier (247 vs. 232 cm−1) and dihedral angle (26°) of cyclopentene. DFT calculations also do an excellent job of predicting the vibrational frequencies of the d0, d1, d4, and d8 isotopomers. They have also allowed the reassignments of several of the vibrational frequencies. 相似文献
59.
An algebraic method that includes Gibbs minimization for performing phase equilibrium calculations for any number of components or phases 总被引:1,自引:0,他引:1
Gustavo A. Iglesias-Silva Adrin Bonilla-Petriciolet Philip T. Eubank James C. Holste Kenneth R. Hall 《Fluid Phase Equilibria》2003,210(2):229-245
The most widely used technique for performing phase equilibria calculations is the K-value method (equality of chemical potentials). This paper proposes a more efficient algorithm to achieve the results that includes Gibbs minimization when we know the number of phases. Using the orthogonal derivatives, the tangent plane equation and mass balances, it is possible to reduce the Gibbs minimization procedure to the task of finding the solution of a system of non-linear equations. Such an operation is easier and faster than finding tangents or areas, and appears to converge as fast as the K-value method. Examples illustrate application of the new technique to two and three phases in equilibrium for binary and ternary mixtures. 相似文献
60.