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161.
It has been known for a long time that any real sequence y
1
, . . . ,y
n-1
is the sequence of critical values of some real polynomial. Here we show that any complex sequence w
1
, . . . ,w
n-1
is the sequence of critical values of some complex polynomial. 相似文献
162.
Assuming the Riemann hypothesis, we exhibit large and smallvalues of the derivative of the zeta function evaluated at thenon-trivial zeros of the zeta function. These results are provedby applying Soundararajan's resonance method. 相似文献
163.
164.
研究了水/ 甲苯乳化液中二苯并噻吩( 硫芴) 在分散型钼酸、磷钼酸和四硫钼酸铵催化剂存在下的加氢脱硫反应. 反应在高压釜中于340 ℃及三种不同的气氛即H2 ,H2/H2 O和CO/H2O(CO 和H2O 经水煤气转换反应( WGSR) 产生原位氢) 的存在下进行. 用GC和GCMS鉴定、分析了气体和液体产物的组成. 结果表明: 对硫芴的加氢脱硫反应,在分散型四硫钼酸铵催化剂存在下,原位产生的氢的效果仅比加入的氢气稍好,而在分散型钼酸和磷钼酸催化剂存在下,原位产生的氢远比加入的氢气有效. 实验结果还表明: 硫化氢能显著提高分散型钼酸和磷钼酸催化剂的加氢脱硫活性,但在分散型四硫钼酸铵催化剂存在下,硫化氢能促进加氢反应而抑制氢解反应. 一氧化碳和水均选择性地抑制氢解反应. 相似文献
165.
166.
Tao Song Corey N. W. Lam Dominic C. M. Ng Galina Orlova Julia Laskin De-Cai Fang Ivan K. Chu 《Journal of the American Society for Mass Spectrometry》2009,20(6):972-984
The dissociation of [CuII(L)His]•2+ complexes [L=diethylenetriamine (dien) or 1,4,7-triazacyclononane (9-aneN3)] bears a strong resemblance to the previously reported behavior of [CuII(L)GGH]•2+ complexes. We have used low-energy collision-induced dissociation experiments and density functional theory (DFT) calculations
at the B3LYP/6-31+G(d) level to study the macrocyclic effect of the auxiliary ligands on the formation of His•+ from prototypical [CuII(L)His]•2+ systems. DFT revealed that the relative energy barriers of the same electron-transfer (ET) dissociation pathways of [CuII(9-aneN3)His]•2+ and [CuII(dien)His]•2+ are very similar, with the ET reactions of [CuII(9-aneN3)His]•2+ leading to the generation of two distinct His•+ species; in contrast, the proton transfer (PT) dissociation pathways of [CuII(9-aneN3)His]•2+ and [CuII(dien)His]•2+ differ considerably. The PT reactions of [CuII(9-aneN3)His]•2+ are associated with substantially higher barriers (>13 kcal/mol) than those of [CuII(dien)His]•2+. Thus, the sterically encumbered auxiliary 9-aneN3 ligand facilitates ET reactions while moderating PT reactions, allowing the formation of hitherto nonobservable histidine
radical cations. 相似文献
167.
Paul Ronald Jones Todd E Albanesi Ralph D Gillespie Priscilla C Jones Seik Weng Ng 《应用有机金属化学》1987,1(6):521-528
Six bis(silyl)acetylenes (XMe2Si? C?C? SiMe2X) with the following varied silicon substituents X were prepared: 1 (Me, Me); 2 (H, H); 3 (C1, H); 4 (CI, CI); 5 (MeO, H); 6 (MeO, MeO). While 1 and 2 may be prepared by the reaction of dilithio- or bis(bromomagnesium)-acetylide with the appropriate chlorosilane, similar reactions designed to give 3–6 yielded oligomers, XMe2Si? (? C?C? SiMe2)n? X, 7, X=CI, MeO, as the major products, indicating that the acetylenic functionality on silicon activates the chlorosilane towards nucleophilic substitution. Compounds 3 and 4 were prepared by free radical chlorination of 2. Methanolysis of 3 and 4 gave quantitative yields of 5 and 6 respectively. Compounds 1–6 undergo a Diels–Alder reaction with α-pyrone to produce, after loss of carbon dioxide, bis(silyl)-substituted benzene derivatives. The order of reactivity has been determined to be: 4=6>3=5>1>2, indicating that chloro or alkoxy substituents favor the cycloaddition with 2- pyrone. The adducts formed by compounds 3–6 undergo an unusually facile hydrolysis or elimination to give 1,1,3,3-tetramethyl-1,3-disila-2-oxaindane. 相似文献
168.
169.
Muonium-radicals resulting from insertion into the benzene ring are found to be much more prevalent in allyl benzene (C6H5CH2CH=CH2) than in styrene (C6H5CH=CH2). The salient implication of this comparison is that intramolecular rearrangements preceeded the μSR observation for the
case of styrene. In turn, this suggests that muonium-containing free radicals, as seen directly by kilogauss transverse field
μSR, are not necessarily theprimary radicals. Therefore, the elucidation of mechanism (and identification of the precursor) of Mu-radical formation is further
complicated by the fact that the observations may refer to thermodynamically more stable secondary radicals-those resulting
from a variety of intra-or inter-molecular relaxations or exchanges. Primary kinetic selectivities of thermalized muonium
atom addition reactions can be determined, however, through the substituent effect on the Hammett linear free energy parameter
in dilute solution. Results have been obtained for substituted benzenes and benzoic acids. Muonium apparently has a mild nucleophilic
character. And, most interestingly, this is opposite to that of its heavy isotope hydrogen. 相似文献
170.
J. Nemeth M. Barranco C. Ngô E. Tomasi 《Zeitschrift für Physik A Hadrons and Nuclei》1986,323(4):419-435
A hydrodynamical approach and the Thomas Fermi approximation have been used to study the evolution of hot and compressed nuclei. Spherical symmetry was assumed in the calculation. The dynamical equations have been transformed into “Schrödinger like” equations (using the Madelung transformation) and were solved numerically. Dissipation was simulated in the same way as in the Navier-Stokes equation by introducing shear and bulk viscosities. Global as well as local thermal equilibrium have been studied. The model has been applied to small amplitude oscillations (the breathing mode) and to the stability of hot and compressed nuclei. It was found that compression is more efficient to break nuclei than thermal excitation. The relaxation time for global equilibrium was estimated to be of the order of 10?22 s. It was found that the results obtained in the case of global and local thermal equilibrium are very similar. 相似文献