全文获取类型
收费全文 | 1116篇 |
免费 | 44篇 |
国内免费 | 6篇 |
专业分类
化学 | 894篇 |
晶体学 | 8篇 |
力学 | 20篇 |
数学 | 137篇 |
物理学 | 107篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 16篇 |
2020年 | 29篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 10篇 |
2016年 | 26篇 |
2015年 | 25篇 |
2014年 | 28篇 |
2013年 | 54篇 |
2012年 | 59篇 |
2011年 | 112篇 |
2010年 | 42篇 |
2009年 | 41篇 |
2008年 | 110篇 |
2007年 | 73篇 |
2006年 | 92篇 |
2005年 | 82篇 |
2004年 | 62篇 |
2003年 | 54篇 |
2002年 | 51篇 |
2001年 | 17篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1976年 | 5篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1970年 | 7篇 |
1938年 | 2篇 |
1935年 | 2篇 |
1929年 | 2篇 |
排序方式: 共有1166条查询结果,搜索用时 31 毫秒
121.
Hai Du Ru-Chun Amy Fuh Junzhong Li L. Andrew Corkan Jonathan S. Lindsey 《Photochemistry and photobiology》1998,68(2):141-142
A database of absorption and fluorescence spectra, including molar absorption coefficients and fluorescence quantum yields, has been compiled for 125 photochemically relevant compounds. An accompanying program enables calculation of oscillator strengths, natural radiative lifetimes, transition dipole moments, Forster energy-transfer rates, multicomponent analysis, simulations of fluorescence spectra upon energy transfer among linear arrays of pigments, calculations of blackbody radiator curves at different temperatures and Lorentzian and Gaussian peak distributions. The program runs under Windows 95 and is equipped with extensive literature references and help features. 相似文献
122.
John P. Elder 《Thermochimica Acta》1985,95(1):33-40
FORTRAN software is described which enables the generation of rate of weight change data (DTG) from percentage weight change measurements (TG), obtained under non-isothermal conditions. The program also transposes this information into the dimensionless extent and rate of reaction at unit temperature intervals by means of a cubic spline interpolation. A simple search routine identifies all DTG spikes in the thermogravimetric record, and the temperature and extent of reaction at which the rate attains its maximum value. This total information serves as input data for the kinetic analysis software to be discussed in part II of this communication. An example of the application of this program to the pyrolysis of bituminous coal is presented. 相似文献
123.
Sublette Kerry L. Plato Amy Woolsey Marion Yates R. G. Camp Carl Bair Tom 《Applied biochemistry and biotechnology》1996,57(1):1013-1019
Applied Biochemistry and Biotechnology - Preliminary experiments have shown thatT. denitrificans strain F can be immobilized in DuPont BIO-SEP beads and used to treat refinery spent sulfidic... 相似文献
124.
This paper treats phase separation within the context of the phenomenological Cahn-Hilliard equation, ct = · [M(c)(∂f/∂c - K2c)], where c is the concentration, M(c) is the mobility, and f(c) is homogeneou s free energy, which is assumed here to be a fourth degree polynomial. Natural boundary conditions are introduced. The full set of equilibrium solutions is specified. A comparison theorem for stability criteria which was postulated by Langer is proved here within the framework of the natural boundary conditions. Energy methods are used to define and estimate the limit of monotonic global stability. It is pointed out that within the parameter region where the uniform homogeneous state is the only equilibrium solution, there may still exist some internal “excitable” region in which the homogeneous solution possesses growing fluctuations. Furthermore a periodic instability is shown to exist in the metastable region in addition to the well-known nucleation instability. 相似文献
125.
Robert T. Lalonde Chunfook Wong Amy I-M. Tsai 《Journal of mass spectrometry : JMS》1976,11(2):183-187
The appearance of m/e 228 and 176 ions, useful in ascertaining the presence of the hemiaminal hydroxyl, are discussed for six thiaspirane-type hemiaminals isolated from Nuphar luteum and three epimeric pairs of α-thiohemiaminals derived from (–)-deoxynupharidine. Other groups of ions useful in ascertaining stereochemical differences of the sulfur moiety in α-thiohemiaminals are discussed for the same compounds. One such group of ions is comprised of 248, 246 and 231; a second is 192 and 191. 相似文献
126.
The crystal structure of [(C6H5)3C3CO](C10H8N2)(CO)2MoBr·C6H6 has been determined. The complex crystallizes in the triclinic space groupP ¯1 witha=8.52(1),b=19.42(3),c=10.54(1) Å, =97.4(1), =74.6(1), and =87.5(1)°. There are two formula units per cell. A total of 2924 unique observed reflections was collected photographically using CuK radiation. The structure was refined toR=0.072. The molybdenum atom in this compound can be considered as situated at the center of a very distorted octahedron. The six coordination sites about the metal atom are occupied by two carbonyl groups which share with the bipyridyl the four equatorial positions. The bromine and a -bonded keto-triphenylcyclobutenyl ring take up the two axial positions. There is an 3 interaction between the cyclobutenyl ring and the molybdenum atom. The detailed geometry of the 1-keto-2,3,4-triphenylcyclobutenyl ligand is similar to that found by Coffey (1962) in a cobalt complex. In the present compound the cyclobutenyl ring is slightly puckered with a dihedral angle of 11.05° between the plane which contains the allylic carbon atoms and that containing the ketonic group. Two solvating benzene molecules are centered at the inversion sites in the unit cell. 相似文献
127.
Ira T Elder 《Journal of Mathematical Analysis and Applications》1982,85(2):360-384
In this article we have described an invariant imbedding method for calculating the smallest eigenlength of a singular TPBVP with the singularity at the origin. The invariant imbedding yields a first-order nonlinear equation called a Riccati equation and also gives the initial conditions at the origin for this equation. With the aid of Theorem 8 in Section 3 we numerically integrate the Riccati equation to “blowup” which gives our computed eigenlength.In closing, we would like to comment on the numerical merits of the integration-to-blowup technique. On the basis of the examples presented it appears that this technique combined with the available numerical integrators with variable step size is capable of producing accurate results. The feature of a variable step size is essential as the value of z approaches the actual eigenlength. However, it is desirable to have a priori estimate or bounds of the eigenlength similar to those of Boland and Nelson [2] for the nonsingular case. The singular system, however, presents difficulties due to the lack of sign conditions on the coefficient matrices in obtaining such bounds. Hopefully an investigation of the matrix R(z) will yield these results. 相似文献
128.
J.P. Elder 《Thermochimica Acta》1980,36(1):67-77
A DSC investigation of a thermal energy storage, first-order phase change system has been carried out. The material is a borax—common salt modified sodium sulfate decahydrate system, distributed throughout a fumed silica supporting matrix. The qualitative features of the thermal behavior of the material can be explained in terms of the phase diagram of the sodium sulfate—water peritectic system, modified by the presence of a low-temperature eutectic. Fusion and recrystallization enthalpies have been measured as a function of cycle number. The thermal conversion efficiency of the system is high. Combining these data with specific heat measurements, the calculated storage capacity is in good agreement with published engineering information. 相似文献
129.
ENDOR studies of the ligation and structure of the non-heme iron site in ACC oxidase 总被引:5,自引:0,他引:5
Tierney DL Rocklin AM Lipscomb JD Que L Hoffman BM 《Journal of the American Chemical Society》2005,127(19):7005-7013
Ethylene is a plant hormone involved in all stages of growth and development, including regulation of germination, responses to environmental stress, and fruit ripening. The final step in ethylene biosynthesis, oxidation of 1-aminocyclopropane-1-carboxylic acid (ACC) to yield ethylene, is catalyzed by ACC oxidase (ACCO). In a previous EPR and ENDOR study of the EPR-active Fe(II)-nitrosyl, [FeNO],(7) complex of ACCO, we demonstrated that both the amino and the carboxyl moieties of the inhibitor d,l-alanine, and the substrate ACC by analogy, coordinate to the Fe(II) ion in the Fe(II)-NO-ACC ternary complex. In this report, we use 35 GHz pulsed and CW ENDOR spectroscopy to examine the coordination of Fe by ACCO in more detail. ENDOR data for selectively (15)N-labeled derivatives of substrate-free ACCO-NO (E-NO) and substrate/inhibitor-bound ACCO-NO (E-NO-S) have identified two histidines as protein-derived ligands to Fe; (1,2)H and (17)O ENDOR of samples in D(2)O and H(2)(17)O solvent have confirmed the presence of water in the substrate-free Fe(II) coordination sphere (E-NO). Analysis of orientation-selective (14,15)N and (17)O ENDOR data is interpreted in terms of a structural model of the ACCO active site, both in the presence (E-NO-S) and in the absence (E-NO) of substrate. Evidence is also given that substrate binding dictates the orientation of bound O(2). 相似文献
130.
[Reaction: see text]. Aryl and alkenyl tosylates are easily prepared, inexpensive and, thus, attractive for transition-metal-catalyzed couplings, but their reactivity is low. We report examples of mild, palladium-catalyzed coupling of aryl, alkenyl, and alkyl Grignard reagents with aryl and alkenyl tosylates. The resulting biaryls, vinylarenes, and alkylarenes were isolated in good to excellent yield. These couplings were conducted with a nearly equimolar ratio of the two reactants, and many examples were conducted at room temperature. 相似文献