全文获取类型
收费全文 | 65670篇 |
免费 | 5650篇 |
国内免费 | 4071篇 |
专业分类
化学 | 5076篇 |
晶体学 | 99篇 |
力学 | 4834篇 |
综合类 | 538篇 |
数学 | 12639篇 |
物理学 | 12076篇 |
综合类 | 40129篇 |
出版年
2024年 | 249篇 |
2023年 | 731篇 |
2022年 | 1356篇 |
2021年 | 1527篇 |
2020年 | 1618篇 |
2019年 | 1420篇 |
2018年 | 1408篇 |
2017年 | 1824篇 |
2016年 | 2053篇 |
2015年 | 2079篇 |
2014年 | 3334篇 |
2013年 | 3760篇 |
2012年 | 3880篇 |
2011年 | 4130篇 |
2010年 | 3274篇 |
2009年 | 3923篇 |
2008年 | 3548篇 |
2007年 | 4481篇 |
2006年 | 3866篇 |
2005年 | 3477篇 |
2004年 | 3126篇 |
2003年 | 2737篇 |
2002年 | 2465篇 |
2001年 | 1981篇 |
2000年 | 1846篇 |
1999年 | 1626篇 |
1998年 | 1343篇 |
1997年 | 1181篇 |
1996年 | 1037篇 |
1995年 | 883篇 |
1994年 | 827篇 |
1993年 | 713篇 |
1992年 | 634篇 |
1991年 | 532篇 |
1990年 | 495篇 |
1989年 | 363篇 |
1988年 | 348篇 |
1987年 | 274篇 |
1986年 | 185篇 |
1985年 | 173篇 |
1984年 | 156篇 |
1983年 | 80篇 |
1982年 | 107篇 |
1981年 | 68篇 |
1980年 | 42篇 |
1979年 | 44篇 |
1978年 | 39篇 |
1977年 | 38篇 |
1976年 | 21篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
991.
Shu-Liang Zang Qing-Guo Zhang Ming Huang Bin Wang Jia-Zhen Yang 《Fluid Phase Equilibria》2005,230(1-2):192-196
This paper reports that an ionic liquid (IL) has been prepared by directly mixing InCl3 and 1-methyl-3-ethylimidazolium chloride (EMIC) with molar ratio 1/1 under dry argon atmosphere. The densities, and surface tension of the pure IL were determined at temperature range of 293.15 to 343.15 ± 0.1 K. The volumetric properties and the properties of surface for ionic liquid based on group III were discussed by Glasser's theory and Yang's interstice model. 相似文献
992.
Cellulose: the structure slowly unravels 总被引:5,自引:0,他引:5
ANTOINETTE C. O'SULLIVAN 《Cellulose (London, England)》1997,4(3):173-207
This article attempts to bring together basic and complex information which has been gathered on cellulose structure, principally
that of native cellulose, over the last few decades. Even though advances have been made in the field of crystallography,
powder crystallography cannot yield a definitive cellulose structure and single crystal diffraction is not possible due to
the lack of suitable crystals. Knowledge obtained on the biosynthesis of native cellulose and on the polymorphy of cellulose
and its derivatives help our understanding of ultrastructure. Many inconsistencies between early crystallographic studies
of native cellulose have been clarified by the discovery that two polymorphs (α and β) of cellulose I exist. Models of the
possible ultrastructural arrangements within native cellulose have been put forward over the decades; with advancement in
technology, computer simulations of small and large systems are being created to test the viability of these ultrastructural
models. It is hoped that this review will aid in the understanding of the complexity and uncertainties that still exist in
this subject.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
993.
The Brønsted acidity of the various Si(nAl) sites present in zeolites is evaluated from proton binding energy and LUMO energy calculated by the semiempirical MNDO quantum chemical method. The two calculated energy values both exhibit a linear correlation with the existing 29Si NMR chemical shift and the IR hydroxyl stretching frequency data. The inter-convertibility between different Si(nAl) sites during an alumination or dealumination process is also evaluated based on the calculated substitution energy. The results indicate that alumination processes are less favorable to occur in zeolites than dealumination processes and the latter is more likely to occur for Si(nAl) clusters that contain the maximum number of aluminum nearest neighbors. 相似文献
994.
A new optimization based adaptive control strategy for simulated moving beds (SMBs) is proposed. A linearized reduced order model, which accounts for the periodic nature of the SMB process, is used for online optimization and control. The manipulated variables are the four inlet flow rates, the outputs are the raffinate and extract concentrations. Concentration measurements at the raffinate and extract outlets are used as the feedback information. The state estimate from the periodic Kalman filter is used for the prediction of the outlet concentrations over a chosen horizon. Predicted outlet concentrations are the basis for the calculation of the optimal input adjustments, which maximize the productivity and minimize the desorbent consumption subject to constraints on product purities. The realization of this concept is discussed and the implementation on a virtual eight column SMB platform is assessed, in the case of binary linear systems. For a whole series of typical plant disturbances it is shown that the proposed approach is effective in minimizing off-spec products and in achieving optimal SMB operation, also in the case where there are significant model uncertainties. 相似文献
995.
996.
997.
The alignment of analytical signals is an important preprocessing step when further analysis (e.g. PCA) requires the same lengths of all of them. Two techniques for alignment of profiles, namely dynamic time warping (DTW) and correlation optimized warping (COW) were tested and compared. The attention was focused on chromatographic and spectroscopic profiles. Simulated and two sets of real data were studied in this study. 相似文献
998.
Oliveira SC Paiva TC Visconti AE Giudici R 《Applied biochemistry and biotechnology》1998,74(3):161-172
Discrimination between different rival models for describing the inhibitory effect of ethanol both on yeast growth and on
fermentation was studied for a continuous process of alcoholic fermentation in a tower reactor with recycling of flocculating
cells. Models tested include linear, parabolic, hyperbolic, exponential, and generalized nonlinear power-law types. The best
expressions were identified under the criteria that all the kinetic parameters should assume acceptable values in a feasible
range and should result in the best fit of the experimental data. The kinetic parameters were estimated from steady-state
data of several sugar concentrations in feeding stream (S0 = 160, 170, 180, 190, 200 g/L), constant dilution rate (D = 0.2 h-1), recycle ratio (α = 13.6), and temperature (T = 30°C). The best model for the yeast growth was of power-law type, whereas
for the product formation the best model was of linear type. These models were able to reproduce the trends of the process
variables satisfactorily. 相似文献
999.
Christian Borgs Roman Kotecký Salvador Miracle-Solé 《Journal of statistical physics》1991,62(3-4):529-551
Recently, Borgs and Kotecký developed a rigorous theory of finite-size effects near first-order phase transitions. Here we apply this theory to the ferromagneticq-state Potts model, which (forq large andd2) undergoes a first-order phase transition as the inverse temperature is varied. We prove a formula for the internal energy in a periodic cube of side lengthL which describes the rounding of the infinite-volume jumpE in terms of a hyperbolic tangent, and show that the position of the maximum of the specific heat is shifted by
m
(L)=(Inq/E)L
–d
+O(L
–2d
) with respect to the infinite-volume transition point
t
. We also propose an alternative definition of the finite-volume transition temperature
t
(L) which might be useful for numerical calculations because it differs only by exponentially small corrections from
t
. 相似文献
1000.
Pierre Devillard 《Journal of statistical physics》1991,62(1-2):443-451
We determine by Monte Carlo simulations the width of an interface between the stable phase and the metastable phase in a two-dimensional Ising model with a magnetic field, in the case of nonconversed order parameter (Glauber dynamics). At zero temperature, the width increases ast
with–1/3, as predicted by earlier theories. As temperature increases, the value of the effective exponent that we measure decreases toward the value 1/4, which is the value in the absence of magnetic field. 相似文献