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101.
William E. Hunter Jerry L. Atwood G. Fachinetti C. Floriani 《Journal of organometallic chemistry》1981,204(1):67-74
The crystal and molecular structure of (η5-C5H5)2Zr[C4(C6H5)4] has been determined by single crystal X-ray diffraction methods. The compound is isostructural with its titanium and hafnium analogues, and crystallizes in the monoclinic space group P21/n with unit cell parameters a = 13.790(5), b = 11.136(5), c = 18.692(7) », β = 92.82(4)°, and ?calc = 1.34 g cm?3 for Z = 4. Full-matrix least-squares refinement converged with a conventional R value of 0.049 for 2986 observed reflections. The metallocyclic ring is planar to within 0.05 », and the π-electron density is largely localized. The two independent ZrC(σ) bond lengths are 2.250(5) and 2.265(6) ». The ZrC(η5) distances range from 2.482(6) to 2.546(7) », and average 2.521(20) ». A comparison of zirconium- and hafnium-carbon bonds based on the data available shows that for M = Hf the MC bonds are shorter for all cases: C(sp), C(sp2), C(sp3), C(η5). 相似文献
102.
William L. Jolly 《Journal of organometallic chemistry》1979,172(2):C33-C35
Substitution of the hydrogen atoms of the cyclopentadienyl ring of (N, N-dimethylaminomethyl)cymantrene by deuterium changes the direction of orientation of metalation of this amine. 相似文献
103.
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
104.
The theoretically estimated dipole moments of indolizine, imidazo[1,2-a]pyridine, imidazo-[1,5-a]pyridine and of pyrazolo[ 1,5-a]pyridine obtained by the CNDO/2 approximation have been compared with the experimental values. The bond angles and bond distances for these polyazaindenes have been estimated. 相似文献
105.
Draper WM 《The Analyst》2002,127(10):1370-1374
Rotenone and piperonyl butoxide (PBO) mixtures, so-called "synergized" rotenone, are invaluable in fisheries management where they are used to protect the habitat of endangered, native species and promote desirable gamefish populations. Continued use of synergized rotenone is threatened by inadequate control of persistence in surface water, especially where drinking water supplies are impacted. The photochemical kinetics of these chemicals were studied in the laboratory with a goal to better understand their fate in natural water. Disappearance quantum yields (phi) were determined in polychromatic light from fluorescent lamps emitting maximally at 350 nm. Rotenone, PBO and trifluralin, an actinometer, were irradiated as aqueous solutions at 25 or 50 microg L(-1) and the piscicides were determined by electrospray-liquid chromatography-mass spectrometry (ESI-LC-MS). In the photoreactor rotenone and PBO photodegraded with first-order half-lives of 500 and 220 min, respectively, and corresponding quantum yields of 0.00015 and 0.034. Rotenone absorbs sunlight strongly, while PRO does not. Differences in spectal overlap tended to counteract the disparities in phi and, in general, mathematical modeling indicates moderately rapid direct photolysis rates for both substances in surface water. 相似文献
106.
Daniel William Tholen 《Accreditation and quality assurance》1998,3(9):362-366
There are three stages to evaluating a laboratory's results in an interlaboratory proficiency test: establishing the correct
result for the test item, determining an evaluation statistic for the particular result, and establishing an acceptable range.
There are a wide variety of procedures for accomplishing these three stages and a correspondingly wide variety of statistical
techniques in use. Currently in North America the largest number of laboratory proficiency test programs are in the clinical
laboratory field, followed by programs for environmental laboratories that test drinking water and waste water. Proficiency
testing in both of these fields is under the jurisdiction of the federal government and other regulatory and accreditation
agencies. Many of the statistical procedures are specified in the regulations, to assure comparability of different programs
and a fair evaluation of performance. In this article statistical procedures recommended in International Organization for
Standardization Guide 43, Part 1, are discussed and compared with current practices in North America.
Received: 22 April 1998 · Accepted: 12 May 1998 相似文献
107.
Siya Ram William Evans Dean S. Wise Leroy B. Townsend John W. Mccall 《Journal of heterocyclic chemistry》1989,26(4):1053-1059
A series of methyl 2-substituted purine 8-carbamates was prepared and evaluated for antifilarial activity. These purines were synthesized as aza congeners of benzimidazole carbamates which have shown significant anthelmintic activity to determine the effect that this modification might have on anthelmintic activity. The compounds were tested against the filarial infection, B. pahangi, in jirds. None of the compounds prepared in this study demonstrated antifilarial activity. 相似文献
108.
STO -3G minimal basis sets for first- and second-row transition metals have been formulated and applied to the calculation of equilibrium geometries for a variety of inorganic systems, metal carbonyls, and organometallic compounds. While the overall level of agreement with experiment is not as good as that previously noted for main-group compounds, most trends and many subtle features in geometries are reproduced. 相似文献
109.
Recalculations of the Gurney free-energy parameters Aij based on the cosphereoverlap model of Friedman and co-workers have been made using more recent experimental data. Our procedure for calculation seems to be more systematic than those previously reported. The excess energy, entropy, and volume parameters (Eij, TSij, and Vij) were also recalculated for some aqueous tetraalkylammonium halides. In addition, the excess-heat-capacity parameters Cij are also reported here for the first time. These data are discussed briefly in terms of the structural implications. 相似文献
110.
Saracoglu N Talaz O Azizoglu A Watson WH Balci M 《The Journal of organic chemistry》2005,70(14):5403-5408
[reaction: see text] endo- and exo-2,3,4,7-tetrahydro-1H-1,4-methanobenzocycloheptene-7-carboxylic acid ethyl esters have been synthesized, and their Diels-Alder cycloaddition reactions with maleic anhydride, dimethyl acetylenedicarboxylate and singlet oxygen have been investigated. The X-ray analysis of four adducts indicated the pyramidalization of the central double bond. Density functional theory calculations on the isolated products and model compounds showed excellent agreement between the experimental and theoretical determined butterfly angles. Furthermore, it has been shown that a cyclopropyl group fused to [2.2.2] system decreases significantly the degree of the pyramidalization which is attributed to the steric interactions between the cyclopropyl group and ethano bridge of the norbornene systems. Due to the instability of the bicyclic endoperoxides, their X-ray analysis could not be carried out. DFT calculations on model compounds showed increased bending in the case of the product obtained by the addition of singlet oxygen to endo-2,3,4,7-tetrahydro-1H-1,4-methanobenzocycloheptene-7-carboxylic acid ethyl ester. 相似文献