全文获取类型
收费全文 | 5381篇 |
免费 | 114篇 |
国内免费 | 18篇 |
专业分类
化学 | 3863篇 |
晶体学 | 19篇 |
力学 | 125篇 |
数学 | 614篇 |
物理学 | 892篇 |
出版年
2022年 | 40篇 |
2021年 | 39篇 |
2020年 | 63篇 |
2019年 | 52篇 |
2016年 | 123篇 |
2015年 | 93篇 |
2014年 | 104篇 |
2013年 | 209篇 |
2012年 | 211篇 |
2011年 | 323篇 |
2010年 | 176篇 |
2009年 | 161篇 |
2008年 | 297篇 |
2007年 | 235篇 |
2006年 | 254篇 |
2005年 | 204篇 |
2004年 | 217篇 |
2003年 | 148篇 |
2002年 | 163篇 |
2001年 | 109篇 |
2000年 | 106篇 |
1999年 | 83篇 |
1998年 | 70篇 |
1997年 | 91篇 |
1996年 | 89篇 |
1995年 | 93篇 |
1994年 | 99篇 |
1993年 | 98篇 |
1992年 | 64篇 |
1991年 | 80篇 |
1990年 | 65篇 |
1989年 | 70篇 |
1988年 | 74篇 |
1987年 | 66篇 |
1986年 | 54篇 |
1985年 | 80篇 |
1984年 | 63篇 |
1983年 | 65篇 |
1982年 | 61篇 |
1981年 | 73篇 |
1980年 | 62篇 |
1979年 | 49篇 |
1978年 | 38篇 |
1977年 | 40篇 |
1976年 | 51篇 |
1975年 | 43篇 |
1974年 | 39篇 |
1973年 | 45篇 |
1970年 | 32篇 |
1967年 | 31篇 |
排序方式: 共有5513条查询结果,搜索用时 0 毫秒
991.
Braun L Liptau P Kehr G Ugolotti J Fröhlich R Erker G 《Dalton transactions (Cambridge, England : 2003)》2007,(14):1409-1415
Treatment of acetonitrile (1 equiv.) with n-butyllithium (0.95 equiv.) followed by chlorodiphenylphosphine (0.95 equiv.) under optimised reaction conditions gave a ca. 60% yield of bis(diphenylphosphino)acetonitrile (dppmCN, 1). The bidentate ligand was employed in the synthesis of the four-membered chelate metal complexes (dppmCN)MCl(2) [M = Pd (6a), Pt (6b)] and (dppmCN)RuCp*(Cl) (7). A very active catalyst for bromobenzene/phenylboronic acid Suzuki-Miyaura coupling was in situ generated by treatment of Pd(OAc)(2) with bis(diphenylphosphino)acetonitrile [TOF (1 h) >600000]. 相似文献
992.
Lüder K Lindfors L Westergren J Nordholm S Kjellander R 《The journal of physical chemistry. B》2007,111(25):7303-7311
The solubility of drugs in water is investigated in a series of papers. In this work, we address the process of bringing a drug molecule from the vapor into a pure drug amorphous phase. This step enables us to actually calculate the solubility of amorphous drugs in water. In our general approach, we, on one hand, perform rigorous free energy simulations using a combination of the free energy perturbation and thermodynamic integration methods. On the other hand, we develop an approximate theory containing parameters that are easily accessible from conventional Monte Carlo simulations, thereby reducing the computation time significantly. In the theory for solvation, we assume that DeltaG* = DeltaGcav + ELJ + EC/2, where the free energy of cavity formation, DeltaGcav, in pure drug systems is obtained using a theory for hard-oblate spheroids, and ELJ and EC are the Lennard-Jones and Coulomb interaction energies between the chosen molecule and the others in the fluid. The theoretical predictions for the free energy of solvation in pure amorphous matter are in good agreement with free energy simulation data for 46 different drug molecules. These results together with our previous studies support our theoretical approach. By using our previous data for the free energy of hydration, we compute the total free energy change of bringing a molecule from the amorphous phase into water. We obtain good agreement between the theory and simulations. It should be noted that to obtain accurate results for the total process, high precision data are needed for the individual subprocesses. Finally, for eight different substances, we compare the experimental amorphous and crystalline solubility in water with the results obtained by the proposed theory with reasonable success. 相似文献
993.
Roland K. W. Roeder 《Journal of Geometric Analysis》2007,17(1):107-146
Little is known about the global structure of the basins of attraction of Newton’s method in two or more complex variables.
We make the first steps by focusing on the specific Newton mapping to solve for the common roots of P(x, y) = x(1−x) and Q(x,
y) = y2 + Bxy − y.
There are invariant circles S0 and S1 within the lines x = 0 and x = 1 which are superattracting in the x-direction and hyperbolically repelling within the vertical
line. We show that S0 and S1 have local super-stable manifolds, which when pulled back under iterates of N form global super-stable spaces W0 and W1. By blowing-up the points of indeterminacy p and q of N and all of their inverse images under N we prove that W0 and W1 are real-analytic varieties.
We define linking between closed 1-cycles in Wi (i = 0, 1) and an appropriate closed 2 current providing a homomorphism lk: H1 (Wi, ℤ) → ℚ. If Wi intersects the critical value locus of N, this homomorphism has dense image, proving that H1 (Wi, ℤ) is infinitely generated. Using the Mayer-Vietoris exact sequence and an algebraic trick, we show that the same is true
for the closures of the basins of the roots
相似文献
994.
T. von Egidy P. Figuera J. Galin F. Goldenbaum Ye. S. Golubeva M. Hasinoff D. Hilscher A. S. Iljinov U. Jahnke M. Krause W. Kurcewicz X. Ledoux B. Lott L. Maier M. Manrique de Lara G. Pausch L. Pienkowski B. Quednau W. Schott W. U. Schröder J. Tõke 《The European Physical Journal A - Hadrons and Nuclei》2000,8(2):197-204
Inclusive neutron energy spectra were measured by time of flight using 1.22 GeV antiprotons from LEAR, CERN, as projectiles
and targets from natural Al, Cu, Ag, Ho, Ta, Au, Pb, Bi, U. The sum of two Maxwellian distributions was fitted to the spectra
obtained at several forward and backward angles yielding neutron multiplicities Mi and slope or temperature parameters T
i for the low-energy (evaporative, i=1) and high-energy (pre-equilibrium,i=2) parts, respectively. M
1 increases with A, proportional to the nuclear volume, and M
2 is growing with A
, proportional to the nuclear radius. The T parameters are nearly independent of A. The results are compared with previous multiplicity measurements with a neutron detector, intranuclear cascade calculations and neutron spectra from stopped antiproton annihilation on nuclei. With
the measured proton spectra also the ratio of emitted neutrons to protons was determined for Au.
Received: 25 February 2000 / Accepted: 19 May 2000 相似文献
995.
G.M. Marshall T.A. Porcelli A. Adamczak J.M. Bailey G.A. Beer M.P. Faifman M.C. Fujiwara T.M. Huber R. Jacot-Guillarmod P. Kammel S.K. Kim P.E. Knowles A.R. Kunselman M. Maier V.E. Markushin G.R. Mason F. Mulhauser A. Olin C. Petitjean J. Zmeskal 《Hyperfine Interactions》1999,118(1-4):89-101
Solid hydrogen in the form of an inhomogeneous layered target offers several experimental advantages when compared with liquid
or gas. Beams of non-thermalized muonic hydrogen atoms allow us to explore resonant molecular ion formation processes near
eV kinetic energies. Isotopically specific layers make it possible to separate competing and confusing interactions and to
employ the time of flight for comparison with predictions based on theoretical energy dependences. Unambiguous charged fusion
product detection simplifies absolute intensity measurements.
The systematic uncertainties encountered in resonant molecular ion formation measurements, using solid hydrogen target layers,
are being investigated with simulations which use the many calculated energy-dependent rates and cross-sections which are
now available. The importance of the rates for processes such as muon transfer and elastic scattering are discussed, and results
of some recent analyses are presented.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
996.
This contribution is devoted to a new feedforward control concept for the thickness control in a hot rolling mill. The core of this concept is an accurate forward slip model for the calculation of the entry thickness profile. This forward slip is derived by means of the fundamental equations of hydrodynamics for a viscoplastic material in the roll gap. The proposed control strategy advantageously uses the additional information of the rolled plate in form of this entry thickness profile. Simulated and measured data demonstrate the feasibility of the forward slip model and the control concept. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
997.
998.
999.