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81.
82.
A general method has been developed for the asymmetric synthesis of 3-vinylidene tetrahydropyrans and 3-vinylidene oxepanes based on the Lewis acid-catalyzed intramolecular reactions of oxocarbenium ions with propargylsilanes. The observed excellent diastereoselectivity and a high asymmetric induction offer a new synthetic method with a wide scope and generality. 相似文献
83.
Mattheus W Masschelein J Gao LJ Herdewijn P Landuyt B Volckaert G Lavigne R 《Chemistry & biology》2010,17(10):1067-1071
BatG is a trans-2-enoyl-ACP reductase, encoded in?the kalimantacin/batumin (kal/bat) biosynthesis operon. It is not essential for the production of the kal/bat secondary metabolite. Instead, BatG is an isoform of FabI, conferring full resistance to target bacteria. It also complements FabI in its role in fatty acid biosynthesis. The identification of FabI as the antibacterial target is important to assess clinical potential of the kalimantacin/batumin antibiotics against Staphylococcus aureus. 相似文献
84.
Halewyck H Oita I Thys B Dejaegher B Vander Heyden Y Rombaut B 《Electrophoresis》2010,31(19):3281-3287
Poliovirions, purified from infected cell extracts with anion-exchange chromatography, can be analyzed and identified by CE in untreated fused silica capillaries using UV detection. Other subviral particles can be eluted as well from the same infected cell extract using a higher salt concentration buffer on the ion-exchange chromatography. Virions can be identified because of their conversion into empty capsids upon heating at 56°C. As a result of heating, the viral genome is released from the capsid. Here, we show that during this incubation some intermediate particles were found. The latter were identified by enzymatic peak shift analysis. The high salt concentration eluate subviral particles were analyzed with preincubation affinity CE together with their sensitivity for RNase and proteinase K treatment. Electropherograms of the higher salt concentration eluate display a mixture of at least four different subviral particles. One particle proved to have an [N1, H] antigenicity and was resistant to RNase and proteinase K digestion. The remaining particles were all sensitive to proteinase K treatment. This CE method proved to be valuable in the detection, identification and analysis of poliovirions and poliovirus particles offering an alternative powerful, cheap, fast and easy analysis method. 相似文献
85.
Bart Mennink 《Designs, Codes and Cryptography》2014,73(1):121-150
We present a collision and preimage security analysis of MDC-4, a 24-years-old construction for transforming an n-bit block cipher into a 2n-bit hash function. We start with MDC-4 based on one single block cipher, and prove that any adversary with query access to the underlying block cipher requires at least \(2^{5n/8}\) queries (asymptotically) to find a collision. For the preimage resistance, we present a surprising negative result: for a target image with the same left and right half, a preimage for the full MDC-4 hash function can be found in \(2^n\) queries. Yet, restricted to target images with different left and right halves, we prove that at least \(2^{5n/4}\) queries (asymptotically) are required to find a preimage. Next, we consider MDC-4 based on two independent block ciphers, a model that is less general but closer to the original design, and prove that the collision bound of \(2^{5n/8}\) queries and the preimage bound of \(2^{5n/4}\) queries apply to the MDC-4 compression function and hash function design. With these results, we are the first to formally confirm that MDC-4 offers a higher level of provable security compared to MDC-2. 相似文献
86.
Bart J. Crielaard Cristianne J. F. Rijcken Lingdong Quan Steffen vanderWal Isil Altintas Martin vanderPot John A. W. Kruijtzer Rob M. J. Liskamp Raymond M. Schiffelers Cornelus F. vanNostrum Wim E. Hennink Dong Wang Twan Lammers Gert Storm 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(29):7366-7370
87.
Diederik Aerts Bart D’Hooghe Emmanuel Haven 《International Journal of Theoretical Physics》2010,49(12):2971-2990
We prove a theorem which shows that a collection of experimental data of probabilistic weights related to decisions with respect
to situations and their disjunction cannot be modeled within a classical probabilistic weight structure in case the experimental
data contain the effect referred to as the ‘disjunction effect’ in psychology. We identify different experimental situations
in psychology, more specifically in concept theory and in decision theory, and in economics (namely situations where Savage’s
Sure-Thing Principle is violated) where the disjunction effect appears and we point out the common nature of the effect. We
analyze how our theorem constitutes a no-go theorem for classical probabilistic weight structures for common experimental
data when the disjunction effect is affecting the values of these data. We put forward a simple geometric criterion that reveals
the non classicality of the considered probabilistic weights and we illustrate our geometrical criterion by means of experimentally
measured membership weights of items with respect to pairs of concepts and their disjunctions. The violation of the classical
probabilistic weight structure is very analogous to the violation of the well-known Bell inequalities studied in quantum mechanics.
The no-go theorem we prove in the present article with respect to the collection of experimental data we consider has a status
analogous to the well known no-go theorems for hidden variable theories in quantum mechanics with respect to experimental
data obtained in quantum laboratories. Our analysis puts forward a strong argument in favor of the validity of using the quantum
formalism for modeling the considered psychological experimental data as considered in this paper. 相似文献
88.
Prof. Dr. Karen Hemelsoet Qingyun Qian Thierry De Meyer Kristof De Wispelaere Dr. Bart De Sterck Prof. Dr. Bert M. Weckhuysen Prof. Dr. Michel Waroquier Prof. Dr. Veronique Van Speybroeck 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16595-16606
The optical absorption properties of (poly)aromatic hydrocarbons occluded in a nanoporous environment were investigated by theoretical and experimental methods. The carbonaceous species are an essential part of a working catalyst for the methanol‐to‐olefins (MTO) process. In situ UV/Vis microscopy measurements on methanol conversion over the acidic solid catalysts H‐SAPO‐34 and H‐SSZ‐13 revealed the growth of various broad absorption bands around 400, 480, and 580 nm. The cationic nature of the involved species was determined by interaction of ammonia with the methanol‐treated samples. To determine which organic species contribute to the various bands, a systematic series of aromatics was analyzed by means of time‐dependent density functional theory (TDDFT) calculations. Static gas‐phase simulations revealed the influence of structurally different hydrocarbons on the absorption spectra, whereas the influence of the zeolitic framework was examined by using supramolecular models within a quantum mechanics/molecular mechanics framework. To fully understand the origin of the main absorption peaks, a molecular dynamics (MD) study on the organic species trapped in the inorganic host was essential. During such simulation the flexibility is fully taken into account and the effect on the UV/Vis spectra is determined by performing TDDFT calculations on various snapshots of the MD run. This procedure allows an energy absorption scale to be provided and the various absorption bands determined from in situ UV/Vis spectra to be assigned to structurally different species. 相似文献
89.
90.
In this work, a novel flow-through solid-phase based chemiluminescence (CL) optical sensor is described for the trace determination of orthophosphate in waters exploiting the multisyringe flow injection analysis (MSFIA) concept with multicommutation. The proposed time-based injection flow system relies upon the in-line derivatisation of the analyte with ammonium molybdate in the presence of vanadate, and the transient immobilisation of the resulting heteropolyacid in a N-vinylpyrrolidone/divinylbenzene copolymer packed spiral shape flow-through cell located in front of the window of a photomultiplier tube. The simultaneous injection of well-defined slugs of luminol in alkaline medium and methanol solution towards the packed reactor is afterwards performed by proper switching of the solenoid valves. Then, the light emission from the luminol oxidation by the oxidant species retained onto the sorbent material is readily detected. At the same time, the generated molybdenum-blue compound is eluted by the minute amount of injected methanol, rendering the system prepared for a new measuring cycle. Therefore, the devised sensor enables the integration of the solid-phase CL reaction with elution and detection of the emitted light without the typical drawbacks of the molybdenum-blue based spectrophotometric procedures regarding the excess of molybdate anion, which causes high background signals due to its self-reduction. The noteworthy features of the developed CL-MSFIA system are the feasibility to accommodate reactions with different pH requirements and the ability to determine trace levels of orthophosphate in high silicate content samples (Si/P ratios up to 500). Under the optimised conditions, a dynamic linear range from 5 to 50 μg P l−1 for a 1.8 ml sample, repeatability better than 3.0% and a quantification limit of 4 μg P l−1 were attained. The flowing stream system handles 11 analysis h−1 and has been successfully applied to the determination of trace levels of orthophosphate in environmental samples such as mineral, ground, tap and pond waters as well as samples from a water-steam cycle of an incineration plant. The t-test comparison of the means for the developed optical sensor and the molybdenum-blue spectrophotometric APHA/AWWA/WPCF reference method revealed that there is no evidence of significant differences between the obtained results at the 95% confidence level. 相似文献