全文获取类型
收费全文 | 10435篇 |
免费 | 448篇 |
国内免费 | 49篇 |
专业分类
化学 | 8266篇 |
晶体学 | 67篇 |
力学 | 179篇 |
数学 | 1330篇 |
物理学 | 1090篇 |
出版年
2023年 | 101篇 |
2022年 | 317篇 |
2021年 | 490篇 |
2020年 | 304篇 |
2019年 | 291篇 |
2018年 | 263篇 |
2017年 | 223篇 |
2016年 | 427篇 |
2015年 | 326篇 |
2014年 | 434篇 |
2013年 | 690篇 |
2012年 | 760篇 |
2011年 | 805篇 |
2010年 | 534篇 |
2009年 | 414篇 |
2008年 | 664篇 |
2007年 | 631篇 |
2006年 | 548篇 |
2005年 | 442篇 |
2004年 | 411篇 |
2003年 | 292篇 |
2002年 | 251篇 |
2001年 | 125篇 |
2000年 | 92篇 |
1999年 | 70篇 |
1998年 | 69篇 |
1997年 | 52篇 |
1996年 | 77篇 |
1995年 | 50篇 |
1994年 | 47篇 |
1993年 | 53篇 |
1992年 | 47篇 |
1991年 | 43篇 |
1990年 | 39篇 |
1989年 | 44篇 |
1988年 | 29篇 |
1987年 | 37篇 |
1986年 | 32篇 |
1985年 | 56篇 |
1984年 | 37篇 |
1983年 | 24篇 |
1982年 | 38篇 |
1981年 | 29篇 |
1980年 | 34篇 |
1979年 | 19篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 16篇 |
1975年 | 10篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Piero Pino Felix Oldani Giambattista Consiglio 《Journal of organometallic chemistry》1983,250(1):491-497
In the hydroformylation of ethylene with approximately equimolar H2/D2 mixtures and Rh4(CO)12 or Co2(CO)8 as the catalyst precursor about 50% of propionaldehyde-d1 was formed. The propionaldehyde-d0/d2 ratio was ~ 3 for rhodium and ~ 2.6 for the cobalt catalyst. On the basis of the results and assuming that there is no rapid M(H)2/M(D)2 scrambling, activation of hydrogen through M(H)2 or M(H)2(olefin) complexes can be excluded. 相似文献
92.
Jo E Sanna MG Gonzalez-Cabrera PJ Thangada S Tigyi G Osborne DA Hla T Parrill AL Rosen H 《Chemistry & biology》2005,12(6):703-715
The essential role of the sphingosine 1-phosphate (S1P) receptor S1P(1) in regulating lymphocyte trafficking was demonstrated with the S1P(1)-selective nanomolar agonist, SEW2871. Despite its lack of charged headgroup, the tetraaromatic compound SEW2871 binds and activates S1P(1) through a combination of hydrophobic and ion-dipole interactions. Both S1P and SEW2871 activated ERK, Akt, and Rac signaling pathways and induced S1P(1) internalization and recycling, unlike FTY720-phosphate, which induces receptor degradation. Agonism with receptor recycling is sufficient for alteration of lymphocyte trafficking by S1P and SEW2871. S1P(1) modeling and mutagenesis studies revealed that residues binding the S1P headgroup are required for kinase activation by both S1P and SEW2871. Therefore, SEW2871 recapitulates the action of S1P in all the signaling pathways examined and overlaps in interactions with key headgroup binding receptor residues, presumably replacing salt-bridge interactions with ion-dipole interactions. 相似文献
93.
Liu Y Vinje J Pacifico C Natile G Sletten E 《Journal of the American Chemical Society》2002,124(43):12854-12862
The reactions of the anticancer complex trans-[PtCl2{(E)-HN=C(OMe)Me}2] (trans-EE) with a series of ribo and deoxyribodinucleotides have been studied by HPLC and 2D [1H, 15N] HMQC NMR spectroscopy and compared with those of the inactive trans isomer of cisplatin, trans-[PtCl2(NH3)2] (trans-DDP). Reactions of trans-EE with r(ApG) and d(ApG) take place through solvolysis of the starting substrate and subsequent formation of trans G-N7/monochloro and G-N7/monoaqua adducts. Slowly, the monofunctional adducts evolve to a bifunctional adduct forming an unprecedented and unexpected A-N3/G-N7 platinum cross-link spanning two trans positions. For stereochemical reasons, trans platinum complexes cannot form N7/N7 cross-links between adjacent purines in di- or polynucleotides. For the reverse sequence r(GpA), no chelate structure was formed even after a two-week reaction. The reaction of trans-DDP with r(ApG) produces many more products than the analogous reaction with trans-EE. One of these products was identified as the A-N3/G-N7 trans-chelate. 相似文献
94.
Adach Anna Cieślak-Golonka Maria Maciejewska Gabriela 《Transition Metal Chemistry》2003,28(3):247-253
The reduction of CrO3 with an excess of L-cysteine and its interaction with DNA fragments (adenine, adenosine) and ATP nucleotide was studied by analysis of the isolated solid products. The precipitates were characterised by elemental analyses, FAB mass spectral data, spectroscopic methods (u.v.–vis., f.i.r., i.r.) and magnetic measurements. The CrIII complexes obtained appear to be various CrIII cysteinate and adenine or ATP (but not adenosine) ternary species of the addition type bound through the hydrogen bonding network. 相似文献
95.
Bernardi A Potenza D Capelli AM García-Herrero A Cañada FJ Jiménez-Barbero J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(20):4598-4612
As a step to delineate a strategy of ligand design for cholera toxin (CT), NMR studies were performed on several mimics of the GM1 ganglioside oligosaccharide. The conformation of these analogues was investigated first in solution and then upon binding to cholera toxin by transferred nuclear Overhauser effect (TR-NOE) measurements. It was demonstrated that CT selects a conformation similar to the global minima of the free saccharides from the ensemble of presented conformations. No evidence of major conformational distortions was obtained, but one or two of the available conformers of the hydroxyacid side chain appear to be selected in the bound state. The NMR data were interpreted with the aid of computer models, generated and analyzed by using a combination of different approaches (MacroModels' MC/EM and MC/SD, Autodock, and GRID). Analysis of the NMR data supported by computational studies allowed us to interpret the experimental observations and to derive workable models of the ligand:toxin complexes. These models suggest that the higher affinity of the (R)-lactic acid derivative 3 may stem from lipophilic interactions with a hydrophobic area in the toxin binding site located in the vicinity of the sialic acid side chain binding region of the CT:GM1 complex, and formed by the side chain of Ile-58 and Lys-34. Thus, the models obtained have allowed us to make useful design suggestions for the improvement of ligand affinity. 相似文献
96.
Amidines can be prepared on a solid support by reducing polymer-bound amidoximes with SnCl2·2H2O. The method has proved to be straightforward and highly efficient. Amidoximes attached to the solid support are readily available by treating resin-bound nitriles with hydroxylamine. 相似文献
97.
Gibasiewicz K Szrajner A Ihalainen JA Germano M Dekker JP van Grondelle R 《The journal of physical chemistry. B》2005,109(44):21180-21186
Almost all photosystem I (PSI) complexes from oxygenic photosynthetic organisms contain chlorophylls that absorb at longer wavelength than that of the primary electron donor P700. We demonstrate here that the low-energy pool of chlorophylls in the PSI-LHCI complex from the green alga Chlamydomonas reinhardtii, containing five to six pigments, is significantly blue-shifted (A(max) at 700 nm at 4 K) compared to that in the PSI core preparations from several species of cyanobacteria and in PSI-LHCI particles from higher plants. This makes them almost isoenergetic with the primary donor. However, they keep the other characteristic features of "red" chlorophylls: clear spectral separation from the bulk chlorophylls, big Stokes shift revealing pronounced electron-phonon coupling, and large homogeneous and inhomogeneous broadening of approximately 170 and approximately 310 cm(-1), respectively. 相似文献
98.
Mafra L Paz FA Shi FN Rocha J Trindade T Fernandez C Makal A Wozniak K Klinowski J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(2):363-375
A compound formulated as (C4H12N2)[Ge2(pmida)2(OH)2] x 4 H2O (where pmida(4-) = N-(phosphonomethyl)iminodiacetate and C4H12N2(2+) = piperazinedium cation), containing the anionic [Ge2(pmida)2(OH)2]2- complex, has been synthesised by the hydrothermal approach and its structure determined by single-crystal X-ray diffraction analysis. Several high-resolution solid-state magic-angle spinning (MAS) NMR techniques, in particular two-dimensional 1H-X(13C,31P) heteronuclear correlation (HETCOR) and 1H-1H homonuclear correlation (HOMCOR) experiments incorporating a frequency-switched Lee-Goldburg (FS-LG) decoupling scheme, have been employed for the first time in such a material. Using these tools in tandem affords an excellent general approach to study the structure of other inorganic-organic hybrids. We assigned the NMR resonances with the help of C...H and P...H internuclear distances obtained through systematic statistical analyses of the crystallographic data. The compound was further characterised by powder X-ray diffraction techniques, IR and Raman spectroscopy, and by elemental and thermal analyses (thermogravimetric analysis and differential scanning calorimetry). 相似文献
99.
[reaction: see text] A simple procedure for the cleavage of triethylsilyl (TES) ethers in the presence of 10 wt % Pd/C in methanol or 95% ethanol is reported. This method allows selective removal of alkyl TES ethers in the presence of aromatic TES ethers or tert-butyldimethylsilyl (TBS) protecting groups. 相似文献
100.
Serganov A Yuan YR Pikovskaya O Polonskaia A Malinina L Phan AT Hobartner C Micura R Breaker RR Patel DJ 《Chemistry & biology》2004,11(12):1729-1741
Metabolite-sensing mRNAs, or "riboswitches," specifically interact with small ligands and direct expression of the genes involved in their metabolism. Riboswitches contain sensing "aptamer" modules, capable of ligand-induced structural changes, and downstream regions, harboring expression-controlling elements. We report the crystal structures of the add A-riboswitch and xpt G-riboswitch aptamer modules that distinguish between bound adenine and guanine with exquisite specificity and modulate expression of two different sets of genes. The riboswitches form tuning fork-like architectures, in which the prongs are held in parallel through hairpin loop interactions, and the internal bubble zippers up to form the purine binding pocket. The bound purines are held by hydrogen bonding interactions involving conserved nucleotides along their entire periphery. Recognition specificity is associated with Watson-Crick pairing of the encapsulated adenine and guanine ligands with uridine and cytosine, respectively. 相似文献