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91.
LETTUCE SEED GERMINATION: EFFECTS OF HIGH TEMPERATURE AND OF REPEATED FAR-RED TREATMENT IN RELATION TO PHYTOCHROME 总被引:5,自引:0,他引:5
Abstract— At 37°C the active form of phytochrome in lettuce seed cannot function to promote subsequent germination. This effect of high temperature is distinct from thermal acceleration of dark reversion from the active form of phytochrome to the inactive form, and may be due to reversible denaturation of phytochrome.
Repeated brief irradiations with far-red light inhibit subsequent germination in the whole seed, whereas a similar irradiation regime results in a strong enhancement of the development of growth potential (ability to expand against an externally-imposed osmotic restraint) in the excised axial portion of the seed. A possible explanation for these two opposing results, in volving two different pigment systems with effective loci in different parts of the seed, is suggested. 相似文献
Repeated brief irradiations with far-red light inhibit subsequent germination in the whole seed, whereas a similar irradiation regime results in a strong enhancement of the development of growth potential (ability to expand against an externally-imposed osmotic restraint) in the excised axial portion of the seed. A possible explanation for these two opposing results, in volving two different pigment systems with effective loci in different parts of the seed, is suggested. 相似文献
92.
Janak KE Tanski JM Churchill DG Parkin G 《Journal of the American Chemical Society》2002,124(16):4182-4183
Mo(PMe3)6 reacts with thiophene to give the eta5-thiophene complex (eta5-C4H4S)Mo(PMe3)3 and the eta5-butadiene-thiolate complex (eta5-C4H5S)Mo(PMe3)2(eta2-CH2PMe2), which are the first examples of (i) eta5-thiophene coordination and (ii) C-S cleavage and hydrogenation by a molybdenum compound. Deuterium labeling studies suggest that the hydrogenation of thiophene may involve an alkylidene intermediate, an observation that has ramifications for the mechanisms of hydrodesulfurization. 相似文献
93.
There are a number of licensed databases that assign biological activities to druglike compounds. The MDL Drug Data Report (MDDR), compiled from the patent literature, is a popular example. It contains several hundred distinct activities, some of which are therapeutic areas (e.g., Antihypertensive) and some of which are related to specific enzymes or receptors (e.g., ACE inhibitor). There are several data mining applications where it would be useful to calculate a similarity between any two activities. Two distinct activity labels can have a significant similarity for a number of reasons: two activities can be nearly synonymous (e.g., CCK B antagonist vs Gastrin antagonist), one activity may be a subset of another (e.g., Dopamine (D2) agonist vs Dopamine agonist), or an activity can be the mechanism by which another activity works (e.g., ACE inhibitor vs Antihypertensive), etc. In an ideal world, similarities for two activities could be calculated simply by comparing the compounds they have in common, but in hand-curated databases such as the MDDR the assignment of activities to compounds are inevitably inconsistent and incomplete. We propose a number of methods of calculating activity-activity similarities that hopefully compensate for errors in hand-curation. Two of these, TIMI and trend vector, show promise. Soft clustering of the activities using a union of similarity methods shows a reasonable association of therapeutic areas with their mechanisms. 相似文献
94.
We measured the fluorescence emission spectrum and intensity decays of methylcyclohexane (MCH) when excited by simultaneous absorption of two photons at 298 nm. The steady-state intensities and lifetimes were both decreased by methanol, which was found to be an efficient quencher of MCH fluorescence. Methanol quenching of MCH is clearly dynamic, but the exact mechanism of quenching is unclear. Dynamic quenching of MCH was also observed by water and n-propanol. These results suggest that alkane fluorescence from biopolymers, if observable, will only occur from regions of the macromolecules that are not exposed to water. 相似文献
95.
DNA oligonucleotides that form intramolecular G-quartet structures were investigated as stationary phase reagents for separation of mixtures of the isomeric dipeptides Trp-Arg and Arg-Trp in open-tubular capillary electrochromatography (OTCEC). The oligonucleotides included a thrombin-binding aptamer that forms a biplanar G-quartet structure and an oligonucleotide that forms a 4-plane G-quartet structure. Fluorescence, circular dichroism and UV-visible absorbance spectroscopies were used in batch solution studies to indicate interactions between the dipeptides and the biplanar G-quartet structure. Results for OTCEC separations were compared with results obtained for capillary zone electrophoresis separations on a bare capillary. Temperature studies suggest that resolution is improved when the G-quartet structure is partially destabilized, but control experiments in which potassium chloride was not included in the mobile phase indicate that the G-quartet structure nevertheless plays a role in the separations. 相似文献
96.
A simple relationship is derived which expresses the change in oscillation frequency of a quartz crystal in contact with a fluid in terms of material parameters of the fluid and the quartz. The relationship is Δf = ?f0(ηL?L/πμQ?Q), where f0 is the oscillation frequency of the free (dry) crystal, ηL and ?L are the absolute viscosity and density of the liquid, respectively, and μQ and ?Q are the elastic modulus and density of the quartz. This relation is obtained from a simple physical model which couples the shear wave in the quartz to a damped shear wave in the fluid. Quantitative comparisons with two test cases, aqueous solutions of glucose and ethanol at various concentrations, demonstrate the accuracy of this model. 相似文献
97.
Itzhak Knigsberg Joseph Jagur-Grodzinski 《Journal of polymer science. Part A, Polymer chemistry》1983,21(9):2649-2663
Monodispersed poly(4-bromostyrenes) (PBs) and their block copolymers with styrene, isoprene, and 3-methylbutene were prepared and characterized by GPC and NMR. Polystyryl and α-methylstyryl carbanions act as effective initiators of the anionic polymerization of Bs in THF. The undersirable side reactions, due to thermally or photochemically induced decomposition of the bromostyryl carbanions, PBs?, may be eliminated by conducting the reaction at ?78°C and in the dark. Under such conditions, the rate constant of propagation, kp (?78°), is 1.5 × 103 M?1 s?1. Radical anions, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Bs}^{\mathop - \limits_ \cdot} $\end{document}, formed as result of electron transfer from sodium naphthalenide to Bs, may eject spontaneously bromine ions. This step and reactions involving the respective phenyl radicals compete at ?78°C with the addition steps leading to polymer formation. Electron affinity of Bs seems to be much higher than that of styrene or isoprene, and PBs? carbanions do not add to the latter monomers. Addition of Bs to polyisoprenyl carbanions leads to formation of the BsIBs block copolymers. BsIBs, prepared in THF, may be converted by preferential hydrogenation of the 1–2 adducts into block copolymers of Bs with poly(2-methylbutene) and isoprenyl segments. The effectiveness of Bs as a flame retarding constituent of polymeric systems seems to be much more pronounced when it is incorporated in a “block” than in a random fashion. A considerably larger fraction of PBs is required to achieve the same LOI value when the respective homopolymers are blended. Spatial distribution of the easily charred microdomains in the block copolymers is believed to be responsible for this phenomenon. 相似文献
98.
Lee Y Hriljac JA Kim SJ Hanson JC Vogt T 《Journal of the American Chemical Society》2003,125(20):6036-6037
The onset of pressure-induced hydration and volume expansion is lowered to 0.6 GPa via the increased flexibility of the host lattice using isomorphous substitution of Al by larger Ga in a sodium aluminosilicate natrolite. 相似文献
99.
A facile synthesis of 3, 5-diamino-1, 2,4-triazines (I) via condensations in acidic media of acylnitriles with aminoguanidine and subsequent base-catalyzed cyclization of the resulting acylnitrile amidinohydrazones (IV) is described. 相似文献
100.
Protein tyrosine nitration is a post-translational modification that occurs under conditions of oxidative stress and may play a role in the pathogenesis of diseases such as asthma. Through their ability to generate reactive oxygen species in macrophages and epithelial cells, particulate pollutants, such as diesel exhaust particles (DEPs), may lead to a worsening of the asthmatic condition. In this study, we looked for evidence of oxidative modification of proteins in RAW 264.7 cell line treated with DEP chemicals. We show that the induction of oxidative stress is accompanied by 53 newly expressed proteins which are suppressed by a thiol antioxidant, N-acetylcysteine. These include antioxidant enzymes, pro-inflammatory components, and products of intermediary metabolism. In addition, inducible nitric oxide synthase (iNOS) was identified as a biologically relevant oxidative stress protein that is induced concurrent with increased NO production and protein tyrosine-nitration in DEP-exposed RAW 264.7 cells. Utilizing two-dimensional gel electrophoresis, anti-nitrotyrosine immunoblotting, and mass spectrometry led to the identification of an additional ten nitrotyrosine modified proteins, including oxidative stress proteins involved in intermediary metabolism (e.g., GAPDH and enolase), antioxidant defense (e.g., MnSOD) and inhibition of proteosomal activity (e.g., Hsp 90alpha). These oxidative proteins may serve as markers for oxidative stress generation in vivo. 相似文献