全文获取类型
收费全文 | 766563篇 |
免费 | 6345篇 |
国内免费 | 2080篇 |
专业分类
化学 | 377253篇 |
晶体学 | 11159篇 |
力学 | 39951篇 |
综合类 | 20篇 |
数学 | 110659篇 |
物理学 | 235946篇 |
出版年
2021年 | 6531篇 |
2020年 | 7007篇 |
2019年 | 7914篇 |
2018年 | 14137篇 |
2017年 | 14500篇 |
2016年 | 16877篇 |
2015年 | 8848篇 |
2014年 | 14236篇 |
2013年 | 33165篇 |
2012年 | 27397篇 |
2011年 | 36010篇 |
2010年 | 25763篇 |
2009年 | 25842篇 |
2008年 | 33053篇 |
2007年 | 34485篇 |
2006年 | 25860篇 |
2005年 | 25482篇 |
2004年 | 22574篇 |
2003年 | 20697篇 |
2002年 | 19731篇 |
2001年 | 21057篇 |
2000年 | 16217篇 |
1999年 | 12504篇 |
1998年 | 10655篇 |
1997年 | 10411篇 |
1996年 | 9877篇 |
1995年 | 8782篇 |
1994年 | 8717篇 |
1993年 | 8406篇 |
1992年 | 9007篇 |
1991年 | 9557篇 |
1990年 | 9118篇 |
1989年 | 8996篇 |
1988年 | 8623篇 |
1987年 | 8568篇 |
1986年 | 8183篇 |
1985年 | 10432篇 |
1984年 | 10860篇 |
1983年 | 9092篇 |
1982年 | 9382篇 |
1981年 | 8801篇 |
1980年 | 8500篇 |
1979年 | 9126篇 |
1978年 | 9364篇 |
1977年 | 9132篇 |
1976年 | 9086篇 |
1975年 | 8717篇 |
1974年 | 8550篇 |
1973年 | 8869篇 |
1972年 | 6349篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Benjamin S. Hsiao Rong-Ming Ho Stephen Z. D. Cheng 《Journal of Polymer Science.Polymer Physics》1995,33(17):2439-2447
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc. 相似文献
912.
Microencapsulation of DNA Within alginate microspheres and crosslinked chitosan membranes for in vivo application 总被引:4,自引:0,他引:4
T. Alexakis D. K. Boadi D. Quong A. Groboillot I. O’Neill D. Poncelet R. J. Neufeld 《Applied biochemistry and biotechnology》1995,50(1):93-106
Calf thymus DNA was microencapsulated within crosslinked chitosan membranes, or immobilized within chitosan-coated alginate
microspheres. Microcapsules were prepared by interfacial polymerization of chitosan, and alginate microspheres formed by emulsification/
internal gelation. Diameters ranged from 20 to 500 Μm, depending on the formulation conditions. Encapsulated DNA was quantifiedin situ by direct spectrophotometry (260 nm) and ethidium bromide fluorimetry, and compared to DNA measurements on the fractions
following disruption and dissolution of the microspheres. Approximately 84% of the DNA was released upon core dissolution
and membrane disruption, with 12% membrane bound. The yield of encapsulation was 96%. Leakage of DNA from intact microspheres/capsules
was not observed. DNA microcapsules and microspheres were recovered intact from rat feces following gavage and gastrointestinal
transit. Higher recoveries (60%) and reduced shrinkage during transit were obtained with the alginate microspheres. DNA was
recovered and purified from the microcapsules and microspheres by chromatography and differential precipitation with ethanol.
This is the first report of microcapsules or microspheres containing biologically active material (DNA) being passed through
the gastrointestinal tract, with the potential for substantial recovery. 相似文献
913.
The microwave subsidiary absorption threshold in tangentially magnetized yttrium-iron-garnet (YIG) films was measured as a function of the static magnetic field, film thickness and decrease in the 0.3–3 μm range is observed. The effect is explained quantitatively by using modified Damon-Eshbach dispersion relations which take into account exchange interactions.
The effect of temperature on hcrit, the smallest threshold field amplitude, in the 250<T< 450 K temperature range can be expressed by an empirical relationship hcrit Ms(T)-1.6 where Ms is the saturation magnetization. This hcrit vs Ms relationship is similar to that obtained for the magnetization dependence of parallel pump thresholds in Li-Ti ferrite compounds. 相似文献
914.
G. S. Kupriyanova 《Applied magnetic resonance》1996,11(1):87-97
A calculation of the complex signals in homonuclear correlation spectra (HOMCOR) of strongly coupled ABX three-spin systems is presented. It is shown that the presence of strong coupling causes the behavior of the cross-peaks to differ significantly from that found in the case of weak coupling. Two classes of connectivity patterns, namely weak and strong connectivity pairs of transitions are distinguished. Closed expressions for the real amplitudes are given. The dependence of the real amplitude on the flip angle of the mixing pulse and on the coupling strength is analyzed. 相似文献
915.
916.
917.
918.
V. S. Kirilyuk 《Journal of Mathematical Sciences》1995,77(6):3486-3488
We consider an elastic isotropic material containing a fibrous inclusion or a void subject to loads. We study the possibility
of increasing the strength of the material using “control action.” As examples of such actions we consider an additional external
load, application of pressure in the cavities (voids), and variation of the temperature of uniform heating of the medium with
the inclusions. Studies are carried out for two-dimensional problems of linear elasticity theory. From the class of all possible
actions we single out a subclass leading to states of equal strength along the phase interface. We study the efficiency of
these types of action and show that in certain cases they lead to a manifold increase in the strength of the material. We
give the results of numerical studies.
Translated fromTeoreticheskaya i Prikladnaya Mekhanika, No. 24, 1993, pp. 15–19. 相似文献
919.
The large N phase transition point is investigated in the heat kernel on the U(N) group with respect to arbitrary boundary conditions. A simple functional relation is found relating the density of eigenvalues of the boundary field to the saddle point shape of the typical Young tableaux in the large N limit of the character expansion of the heat kernel. Both strong coupling and weak coupling phases are investigated for some particular cases of the boundary holonomy. 相似文献
920.