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911.
912.
913.
S. Ulbig K. P. Lieb H. G. Boerner B. Krusche S. J. Robinson J. G. L. Booten 《Zeitschrift für Physik A Hadrons and Nuclei》1991,338(4):397-404
The GRID-method has been used to measure the lifetimes of ten excited states in59, 61, 63Ni following thermal neutron capture in Ni targets of natural isotopic composition. Four of the lifetimes have been determined for the first time, the other six lifetimes can be compared with the results of conventional DSA-measurements following charged particle induced reactions. Cascade feeding effects have been included in the analysis. Level energies and electromagnetic properties of negative parity states in59Ni have been compared with the results of shell model calculations in 3p0h and 4p 1h model spaces. Statistical model estimates of the lifetimes as function of excitation energy and spin are also given.Work partially supported by Deutsches BMFT under contract 06GOE141 相似文献
914.
A highly efficient method is developed for automated high-throughput screening of nanoliter-scale protein crystallization.
The system integrates liquid dispensing, crystallization and detection. The automated liquid dispensing system handles nanoliters
of protein and various combinations of precipitants in parallel to access diverse regions of the phase diagram. A new detection
scheme, native fluorescence, with complementary visible-light detection is employed for monitoring the progress of crystallization.
This detection mode can distinguish protein crystals from inorganic crystals in a nondestructive manner. A gas-permeable membrane
covering the microwells simplifies evaporation rate control and probes extended conditions in the phase diagram. The system
was successfully demonstrated for the screening of lysozyme crystallization under 81 different conditions. 相似文献
915.
Alison J. Downard Brian H. Robinson Jim Simpson 《Journal of organometallic chemistry》1987,320(3):363-384
The generality of a two-electron reduction process involving an
mechanism has been established for M3(CO)12 and M3(CO)12−n(PPh3)n (M = Ru, Os) clusters in all solvents. Detailed coulometric and spectral studies in CH2Cl2 provide strong evidence for the formation of an ‘opened’ M3(CO)122− species the triangulo radical anions M3(CO)12−· having a half-life of < 10−6 s in CH2Cl2. However, the electrochemical response is sensitive to the presence of water and is concentration dependent. An electrochemical response for “opened” M3(CO)122− is only detected at low concentrations < 5 × 10−4 mol dm−3 and under drybox conditions. The electroactive species ground at higher concentrations and in the presence of water M3(CO)112− and M6(CO)182− were confirmed by a study of the electrochemistry of these anions in CH2Cl2; HM3(CO)11− is not a product. The couple [M6(CO)18]−/2− is chemically reversible under certain conditions but oxidation of HM3(CO)11− is chemically irreversible. Different electrochemical behaviour for Ru3(CO)12 is found when [PPN][X] (X = OAc−, Cl−) salts are supporting electrolytes. In these solutions formation of the ultimate electroactive species [μ-C(O)XRu3(CO)10]− at the electrode is stopped under CO or at low temperatures but Ru3(CO)12−· is still trapped by reversible attack by X presumably as [η1-C(O)XRu3(CO)11]−. It is shown that electrode-initiated electron catalysed substitution of M3(CO)12 only takes place on the electrochemical timescale when M = Ru, but it is slow, inefficient and non-selective, whereas BPK-initiated nucleophilic substitution of Ru3(CO)12 is only specific and fast in ether solvents particulary THF. Metal---metal bond cleavage is the most important influence on the rate and specificity of catalytic substitution by electron or [PPN]-initiation. The redox chemistry of M3(CO)12 clusters (M = Fe, Ru, Os) is a consequence of the relative rates of metal---metal bond dissociation, metal-metal bond strength and ligand dissociation and in many aspects resembles their photochemistry. 相似文献
916.
Force constants and compliance constants for the CHX3 and SiHX3 molecules have been obtained, using the vibrational frequencies of CHX3 and CDX3 (SiHX3 and SiDX3) molecules only. The reliability of the resulting force field has been checked by calculation of Coriolis coupling constants, centrifugal distortion constants and mean amplitudes of vibration and by comparison with the available experimental data. 相似文献
917.
Rosen GM Beselman A Tsai P Pou S Mailer C Ichikawa K Robinson BH Nielsen R Halpern HJ MacKerell AD 《The Journal of organic chemistry》2004,69(4):1321-1330
Spin trapping, a technique used to characterize short-lived free radicals, consists of using a nitrone or nitroso compound to "trap" an unstable free radical as a long-lived aminoxyl that can be characterized by EPR spectroscopy. The resultant aminoxyl exhibits hyperfine splitting constants that are dependent on the spin trap and the free radical. Such is the case with 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxyl (DMPO-OH) and 2,2-dimethyl-5-hydroperoxy-1-pyrrodinyloxyl (DMPO-OOH) whose hyperfine splitting constants, A(N) = A(H) = 14.9 G and A(N) = 14.3 G, A(H)(beta) = 11.7 G, and A(H)(gamma) = 1.25 G, respectively, have been used to demonstrate the generation of HO(*) and O(2)(*)(-). However, to date, the source of the apparent A(H)(gamma) hyperfine splitting in DMPO-OOH is not known. We consider three possible explanations to account for the unique EPR spectrum of DMPO-OOH. The first is that the gamma-splitting arises from one of the hydrogen atoms at either carbon 3 or carbon 4 of DMPO-OOH. The second is that the gamma-splitting originates from the hydrogen atom of DMPO-OOH. The third is that the conformational properties of DMPO-R change upon going from DMPO-OH to DMPO-OOH. Experimental and theoretical chemical approaches as well as EPR spectral modeling were used to investigate which of these hypotheses may explain the asymmetric EPR spectrum of DMPO-OOH. From these studies it is shown that the 12-line EPR spectrum of DMPO-OOH results not from any proximal hydrogen, but from additional conformers of DMPO-OOH. Thus, the 1.25 G hyperfine splitting, which has been assigned as a gamma-splitting, is actually from two individual EPR spectra associated with different conformers of DMPO-OOH. 相似文献
918.
Photoenolization as a means to release alcohols 总被引:2,自引:0,他引:2
Pika J Konosonoks A Robinson RM Singh PN Gudmundsdottir AD 《The Journal of organic chemistry》2003,68(5):1964-1972
We have designed molecules which release alcohols upon exposure to UV light independent of the reaction media, making it possible to liberate alcohols in a controlled manner in applications. Photolysis of 2-(2-isopropylbenzoyl)benzoate ester derivatives 4 in various solvents and in thin films results in the liberation of the alcohol moiety from the ester. The reaction mechanism for the release of the alcohol has been elucidated by time-resolved laser flash photolysis. Upon irradiation the triplet excited state of ketone, 4 is formed, and its lifetime can be estimated to be between 0.08 and 0.8 ns. The triplet excited state decays by efficient intramolecular H-atom abstraction to form a 1,4-biradical, 8, that has a lifetime of less than 17 ns and is trapped by molecular oxygen. In the absence of oxygen, biradical 8 intersystem crosses to form photoenols (Z)-9 and (E)-10 in a ratio of 5:2, respectively. Photoenol (Z)-9 has a lifetime of approximately 3000 ns in protic solvents and returns to the starting material through 1,5 intramolecular hydrogen transfer. The other isomer, (E)-10, is much longer lived (>1 ms) and releases the alcohol moiety through an intramolecular lactonization. 相似文献
919.
Derek W. Robinson 《Communications in Mathematical Physics》1982,85(1):129-142
Let (?, τ, ω) denote aW*-algebra ?, a semigroupt>0?τ t of linear maps of ? into ?, and a faithful τ-invariant normal state ω over ?. We assume that τ is strongly positive in the sense that $$\tau _t (A^ * A) \geqq \tau _t (A)^ * \tau _t (A)$$ for allA∈? andt>0. Therefore one can define a contraction semigroupT on ?= \(\overline {\mathcal{M}\Omega } \) by $$T_t A\Omega = \tau _t (A)\Omega ,{\rm A} \in \mathcal{M},$$ where Ω is the cyclic and separating vector associated with ω. We prove 1. the fixed points ?(τ) of τ are given by ?(τ)=?∩T′=?∩E′, whereE is the orthogonal projection onto the subspace ofT-invariant vectors, 2. the state ω has a unique decomposition into τ-ergodic states if, and only if, ?(τ) or {?υE}′ is abelian or, equivalently, if (?, τ, ω) is ?-abelian, 3. the state ω is τ-ergodic if, and only if, ?υE is irreducible or if $$\mathop {\inf }\limits_{\omega '' \in Co\omega 'o\tau } \left\| {\omega '' - \omega '} \right\| = 0$$ for all normal states ω′ where Coω′°τ denotes the convex hull of {ω′°τ t } t>0. Subsequently we assume that τ is 2-positive,T is normal, andT* t ?+Ω \( \subseteqq \overline {\mathcal{M}_ + \Omega } \) , and then prove 4. there exists a strongly positive semigroup |τ| which commutes with τ and is determined by $$\left| \tau \right|_t \left( A \right)\Omega = \left| {T_t } \right|A\Omega ,$$ 5. results similar to 1 and 2 apply to |τ| but the τ-invariant state ω is |τ|-ergodic if, and only if, $$\mathop {\lim }\limits_{t \to \infty } \left\| {\omega 'o\tau _t - \omega } \right\| = 0$$ for all normal states ω′. 相似文献
920.
AIDS is a progressive disease associated with steady loss of helper T cells and several other functions. As the disease evolves, cytopathogenic human immunodeficiency (HIV) variants of increasing virulence can be isolated from the host. The HIV is an unusually variable genome by virtue of a low replication fidelity. In this report we describe our effort to test the hypothesis that there is a correlation between virus variability and cytopathogenicity, and further, that there is an "impact" of the virus infection on the expression of host cellular genes. To search for such a relationship, we infected H-9 cells (human CD4+ lymphoblastoid cell line) with each of 5 isolates of HIV of distinct origin and cytopathogenicity. To measure the influence of the virus infection on the expression of host cellular genes, shortly after infection, (3 h or 13 h), cells were radiolabeled and the radioactive polypeptides separated by two-dimensional gel electrophoresis. Radiofluorographs were prepared and analyzed to determine relative rates of biosynthesis of cellular polypeptides. To organize the large amounts of data found, cluster analysis and principal component analysis were used to expose the data in formats that allowed a model construction. The rates of biosynthesis of many cellular polypeptides were altered upon viral infection in terms of both enhancements and impairment of biosynthesis. Some of the variation in polypeptide synthesis was isolate-specific, while most alterations were of modest magnitude. There appears to be no "overall effect" associated with infection by a cytopathic variant of the virus. Polypeptides affected by the cytopathic variants were determined as targets for further investigation. The method used promotes the measurement of "ensemble" information that is characteristic of the process and it promotes the creation of models of virus action. 相似文献