全文获取类型
收费全文 | 2822篇 |
免费 | 57篇 |
国内免费 | 7篇 |
专业分类
化学 | 1906篇 |
晶体学 | 9篇 |
力学 | 32篇 |
数学 | 542篇 |
物理学 | 397篇 |
出版年
2022年 | 17篇 |
2021年 | 24篇 |
2020年 | 23篇 |
2019年 | 28篇 |
2018年 | 26篇 |
2016年 | 47篇 |
2015年 | 48篇 |
2014年 | 44篇 |
2013年 | 94篇 |
2012年 | 90篇 |
2011年 | 115篇 |
2010年 | 70篇 |
2009年 | 73篇 |
2008年 | 88篇 |
2007年 | 88篇 |
2006年 | 89篇 |
2005年 | 67篇 |
2004年 | 76篇 |
2003年 | 41篇 |
2002年 | 55篇 |
2001年 | 53篇 |
2000年 | 37篇 |
1999年 | 29篇 |
1998年 | 30篇 |
1997年 | 32篇 |
1996年 | 48篇 |
1995年 | 41篇 |
1994年 | 47篇 |
1993年 | 33篇 |
1992年 | 32篇 |
1991年 | 30篇 |
1990年 | 37篇 |
1989年 | 31篇 |
1988年 | 30篇 |
1987年 | 36篇 |
1985年 | 55篇 |
1984年 | 45篇 |
1983年 | 42篇 |
1982年 | 19篇 |
1981年 | 45篇 |
1980年 | 41篇 |
1979年 | 30篇 |
1978年 | 39篇 |
1977年 | 38篇 |
1976年 | 26篇 |
1975年 | 33篇 |
1974年 | 33篇 |
1973年 | 23篇 |
1972年 | 16篇 |
1960年 | 19篇 |
排序方式: 共有2886条查询结果,搜索用时 31 毫秒
31.
Crawford MJ Ellern A Karaghiosoff K Mayer P Nöth H Suter M 《Inorganic chemistry》2004,43(22):7120-7126
The synthesis and characterization of the dioxouranium(VI) dibromide and iodide hydrates, UO(2)Br(2)x3H(2)O (1), [UO(2)Br(2)(OH(2))(2)](2) (2), and UO(2)I(2)x2H(2)Ox4Et(2)O (3), are reported. Moreover, adducts of UO(2)I(2) and UO(2)Br(2) with large, bulky OP(NMe(2))(3) and OPPh(3) ligands such as UO(2)I(2)(OP(NMe(2))(3))(2) (4), UO(2)Br(2)(OP(NMe(2))(3))(2) (5), and UO(2)I(2)(OPPh(3))(2)(6) are discussed. The structures of the following compounds were determined using single-crystal X-ray diffraction techniques: (1) monoclinic, P2(1)/c, a = 9.7376(8) A, b = 6.5471(5) A, c = 12.817(1) A, beta = 94.104(1) degrees , V = 815.0(1) A(3), Z = 4; (2) monoclinic, P2(1)/c, a = 6.0568(7) A, b = 10.5117(9) A, c = 10.362(1) A, beta = 99.62(1) degrees , V = 650.5(1) A(3), Z = 2; (4) tetragonal, P4(1)2(1)2, a = 10.6519(3) A, b = 10.6519(3) A, c = 24.0758(6) A, V = 2731.7(1) A(3), Z = 4; (5) tetragonal, P4(1)2(1)2, a = 10.4645(1) A, b = 10.4645(1) A, c = 23.7805(3) A, V = 2604.10(5) A(3), Z = 4, and (6) monoclinic, P2(1)/c, a = 9.6543(1) A, b = 18.8968(3) A, c = 10.9042(2) A, beta =115.2134(5) degrees , V = 1783.01(5) A(3), Z = 2. Whereas 1 and 2 are the first UO(2)Br(2) hydrates and the last missing members of the UO(2)X(2) hydrate (X = Cl --> I) series to be structurally characterized, 4 and 6 contain room-temperature stable U(VI)-I bonds with 4 being the first structurally characterized room temperature stable U(VI)-I compound which can be conveniently prepared on a gram scale in quantitative yield. The synthesis and characterization of 5 using an analogous halogen exchange reaction to that used for the preparation of 4 is also reported. 相似文献
32.
Zinc Complexes of a New N, N, O Ligand The tridentate ligand N, N(2‐dimethylaminoethyl)‐3, 5‐di‐tert.‐butyl‐salicylaldimine ( L H) results from the corresponding salicylic aldehyde and N, N‐dimethyl ethylenediamine. With zinc salts it forms the mononuclear halide complexes [ L ZnCl ˙ CH3OH] ( 1 ) and [ L ZnI ˙ CH3OH] ( 2 ) and the presumably polymeric acetate [ L ZnOCOCH3] ( 3 ). With diethyl zinc and diphenylphosphoric acid it yields the phosphate complex [ L Zn‐OPO(OPh)2 ˙ CH3OH] ( 4 ). The coordination of the complexes, which is between trigonal bipyramidal and square pyramidal, and the character of the five donors in the phosphate complex represent the transition state of a hydrolytic substrate cleavage in a zinc enzyme. 相似文献
33.
Sucrose ethyleneoxide adducts have been prepared by reaction of sucrose with various amounts of ethyleneoxide inDMSO. The resulting polypode molecules were found to be efficient phase transfer catalysts in nucleophilic substitutions, oxidation and dichlorcarbene generation. Polymerisable polypodes have been obtained by reaction of sucrose ethyleneoxide adducts with methacrylic anhydride or methacryloylchloride in pyridine. Free radical polymerisation of the resulting mixtures of mono- and polyfunctional methacrylic esters of sucrose ethyleneoxide adducts yielded crosslinked gels. These polymer-supported octopus-molecules were found to be efficient triphase catalysts. 相似文献
34.
William Heilman Ernst Kupfer Walter Keller-Schierlein Hans Zhner Heinz Wolf Heinrich H. Peter 《Helvetica chimica acta》1979,62(1):1-6
From cultures of the Avilamycin (Avilamycin A) producing organism, Streptomyces viridochromogenes, strain ETH 23575, a second antibiotic, Avilamycin C, C61H90Cl2O32 could be isolated in crystalline form. Both Avilamycins belong to the group of the Orthosomycins. By IR., 1H- and 13C-NMR. spectroscopy and by transformation to a common derivative it could be proven that Avilamycin A is a methyl ketone, Avilamycin C the corresponding methyl carbinol. 相似文献
35.
Heinrich Hillig Hendrik Küper Wolfgang Riepe Hans Peter Ritter 《Analytica chimica acta》1979,112(2):123-132
Automation of a mass spectrometer—computer system makes it possible to process up to 30 samples without attention after sample loading. An automatic sample changer introduces the samples successively into the ion source by means of a direct inlet probe. A process control unit determines the operation sequence. Computer programs are available for the hardware support, system supervision and evaluation of the spectrometer signals. The most essential precondition for automation — automatic evaporation of the sample material by electronic control of the total ion current — is confirmed to be satisfactory. The system operates routinely overnight in an industrial laboratory, so that day work can be devoted to difficult analytical problems. The cost of routine analyses is halved. 相似文献
36.
On the Reaction of Germanium with Germanium Tetrachloride and on the Existence of the Oxidechlorides GeOCl2 and GeOCl6 at the Equilibrium The above equilibrium was measured in a Gauge-manometer and the enthalpy of formation and the entropy for GeCl2,g were derived from these results. From total pressure measurements and transport experiments of GeO2 with GeCl4 follows, that the oxidechlorides Ge2OCl6 and GeOCl2 are not present in measurable concentrations, that means the enthalpy of formation of GeOCl2 must be higher than ?327 kJ · mol?1. 相似文献
37.
Shawn R. Hitchcock George P. Nora David M. Casper Joseph D. Wiman Jeromy T. Bentley Carrie Stafford Michael D. Squire 《Journal of heterocyclic chemistry》2002,39(5):1113-1115
A several novel 1,3,4‐oxadiazinan‐2‐thiones have been synthesized by the cyclization of β‐hydrazino‐alcohols with either carbon disulfide or 1,1′‐thiocarbonyldiimidazole (TCDI). 相似文献
38.
Information
Congresses, conferences, symposia, meetings, and seminars in the field of chemical sciences held in 1995–1996 相似文献39.
Letf be a meromorphic function of infinite order,T(r, f) its Nevanlinna (or Ahlfors-Shimizu) characteristic, andM(r, f) its maximum modulus. It is proved that $$\mathop {\lim \inf }\limits_{r \to \infty } \frac{{\log M(r,f)}}{{rT'(r,f)}} \leqslant \pi and\mathop {\lim \inf }\limits_{r \to \infty } \frac{{\log M(r,f)}}{{T(r,f)\psi (log T(r,f))}} = 0$$ . if ? (x)/x is non-decreasing, ?′(x)<-√?(x) and ∝∞ dx/?(x) < ∞. 相似文献
40.
van Nostrum CF Benneker FB Brussaard H Kooijman H Veldman N Spek AL Schoonman J Feiters MC Nolte RJ 《Inorganic chemistry》1996,35(4):959-969
The synthesis of novel magnesium, copper, and metal-free porphyrazines, peripherally substituted with dithia-7-crown-2 (MPz(7)), dithia-15-crown-5 (MPz(15)), and dithia-18-crown-6 (MPz(18)) macrocycles is reported. These compounds are prepared starting from dicyanoethylene containing crown ethers 3, 2(1), and 2(2), respectively, which contain sulfur as well as oxygen heteroatoms. The "crowned" porphyrazines bind silver(I) and mercury(II) perchlorates. UV/vis spectroscopy and electron paramagnetic resonance measurements reveal that addition of the transition-metal ions leads to dimerization of the porphyrazine complexes. In the case of the dithia-18-crown-6-substituted porphyrazines, the dimers break up to form monomeric 6:1 guest-host complexes when more than 2 equiv of the metal ion is added. The single-crystal structures of the crown ether 2(2) and the porphyrazine MgPz(18) are presented. Compound C(14)H(20)N(2)O(4)S(2) (2(2)) crystallizes in the monoclinic space group P2(1)/c with a = 10.9310(13) ?, b = 19.383(3) ?, c = 8.6976(14) ?, beta = 108.898(11) degrees, V = 1743.5(5) ?(3), and Z = 4. The structure refinement converged to R = 0.0366 and R(w) = 0.0504. Compound C(56)H(82)MgN(8)O(17)S(8) (MgPz(18)) crystallizes in the triclinic space group P&onemacr; with a = 9.584(3) ?, b = 17.672(2) ?, c = 19.620(4) ?, alpha = 84.904(14) degrees, beta = 85.21(2) degrees, gamma = 89.29(2) degrees, V = 3298.4(13) ?(3), and Z = 2. The structure refinement converged to R1 = 0.0839 and wR2 = 0.2196. The electrical properties of H(2)Pz(18) have been studied by complex impedance spectroscopy. The bulk electrical conductivity of this compound is approximately 1 order of magnitude higher than that of the corresponding 18-crown-6 phthalocyanine. 相似文献