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981.
Dr. C. Frank Lee Dr. Carla E. Brown Dr. Alexander J. Nielsen Changmo Kim Dr. Izhar Livne-Bar Prof. Dr. Philip J. Parsons Dr. Christophe Boldron Dr. François Autelitano Prof. Dr. Donald F. Weaver Prof. Dr. Jeremy M. Sivak Prof. Dr. Mark A. Reed 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(35):e202200360
Two stereocontrolled, efficient, and modular syntheses of eicosanoid lipoxin B4 (LXB4) are reported. One features a stereoselective reduction followed by an asymmetric epoxidation sequence to set the vicinal diol stereocentres. The dienyne was installed via a one-pot Wittig olefination and base-mediated epoxide ring opening cascade. The other approach installed the diol through an asymmetric dihydroxylation reaction followed by a Horner-Wadsworth-Emmons olefination to afford the common dienyne intermediate. Finally, a Sonogashira coupling and an alkyne hydrosilylation/proto-desilylation protocol furnished LXB4 in 25 % overall yield in just 10 steps. For the first time, LXB4 has been fully characterized spectroscopically with its structure confirmed as previously reported. We have demonstrated that the synthesized LXB4 showed similar biological activity to commercial sources in a cellular neuroprotection model. This synthetic route can be employed to synthesize large quantities of LXB4, enable synthesis of new analogs, and chemical probes for receptor and pathway characterization. 相似文献
982.
983.
984.
985.
Trung Le Hao Nguyen Dr. Lisa M. Perez Prof. Donald J. Darensbourg Prof. Marcetta Y. Darensbourg 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3674-3678
With the goal of generating anionic analogues to MN2S2 ⋅ Mn(CO)3Br we introduced metallodithiolate ligands, MN2S22− prepared from the Cys-X-Cys biomimetic, ema4− ligand (ema=N,N′-ethylenebis(mercaptoacetamide); M=NiII, [VIV≡O]2+ and FeIII) to Mn(CO)5Br. An unexpected, remarkably stable dimanganese product, (H2N2(CH2C=O(μ-S))2)[Mn(CO)3]2 resulted from loss of M originally residing in the N2S24− pocket, replaced by protonation at the amido nitrogens, generating H2ema2−. Accordingly, the ema ligand has switched its coordination mode from an N2S24− cavity holding a single metal, to a binucleating H2ema2− with bridging sulfurs and carboxamide oxygens within Mn-μ-S-CH2-C-O, 5-membered rings. In situ metal-templating by zinc ions gives quantitative yields of the Mn2 product. By computational studies we compared the conformations of “linear” ema4− to ema4− frozen in the “tight-loop” around single metals, and to the “looser” fold possible for H2ema2− that is the optimal arrangement for binucleation. XRD molecular structures show extensive H-bonding at the amido-nitrogen protons in the solid state. 相似文献
986.
Trung Le Hao Nguyen Lisa M. Perez Donald J. Darensbourg Marcetta Y. Darensbourg 《Angewandte Chemie (International ed. in English)》2020,59(9):3645-3649
With the goal of generating anionic analogues to MN2S2 ? Mn(CO)3Br we introduced metallodithiolate ligands, MN2S22? prepared from the Cys‐X‐Cys biomimetic, ema4? ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=NiII, [VIV≡O]2+ and FeIII) to Mn(CO)5Br. An unexpected, remarkably stable dimanganese product, (H2N2(CH2C=O(μ‐S))2)[Mn(CO)3]2 resulted from loss of M originally residing in the N2S24? pocket, replaced by protonation at the amido nitrogens, generating H2ema2?. Accordingly, the ema ligand has switched its coordination mode from an N2S24? cavity holding a single metal, to a binucleating H2ema2? with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH2‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn2 product. By computational studies we compared the conformations of “linear” ema4? to ema4? frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H2ema2? that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state. 相似文献
987.
Donald Bedford 《International Journal of Mathematical Education in Science & Technology》2013,44(6):723-727
An elementary analysis of the problem of tides on an ideal Earth from a point of view of the forces involved proves to be a valuable exercise in terms of the applied mathematics as well as the physics. The approximations show their value both for obtaining analytic solutions and for exhibiting the symmetry‐breaking at higher order. 相似文献
988.
General conclusions relating pairwise tallies with positional (e.g., plurality, antiplurality (“vote-for-two”)) election outcomes were previously known only for the Borda Count. While it has been known since the eighteenth century that the Borda and Condorcet winners need not agree, it had not been known, for instance, in which settings the Condorcet and plurality winners can disagree, or must agree. Results of this type are developed here for all three-alternative positional rules. These relationships are based on an easily used method that connects pairwise tallies with admissible positional outcomes; e.g., a special case provides the first necessary and sufficient conditions ensuring that the Condorcet winner is the plurality winner; another case identifies when there must be a profile whereby each candidate is the “winner” with some positional rule. 相似文献
989.
990.
Christine Farthing Don Farthing Donald F. Brophy Terri Larus Lena Maynor Itaf Fakhry Todd W. B. Gehr 《Chromatographia》2008,67(5-6):365-368
A simple high-performance liquid chromatographic (HPLC) method was developed for the simultaneous determination of cefepime
and cefazolin in human plasma and dialysate. For component separation, the method utilized a C18 column with an aqueous mobile phase of dibasic potassium hydrogen phosphate (pH 7.0) and methanol gradient at a flow rate
of 1 mL min−1. The method demonstrated linearity from 2.0 to 100.0 μg mL−1 (r > 0.999) with detection limit of 1 μg mL−1 for both cefepime and cefazolin. The method was utilized for evaluation of plasma and dialysate samples in a clinical study
evaluating the dialyzer clearance of cefepime and cefazolin using high-flux hemodialysis with varying blood flow rates in
chronic kidney failure patients undergoing hemodialysis and peritoneal dialysis treatment. 相似文献