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991.
Dr. David R. Armstrong Jennifer A. Garden Dr. Alan R. Kennedy Sarah M. Leenhouts Prof. Robert E. Mulvey Philip O'Keefe Dr. Charles T. O'Hara Dr. Alan Steven 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(40):13492-13503
Most recent advances in metallation chemistry have centred on the bulky secondary amide 2,2,6,6‐tetramethylpiperidide (TMP) within mixed metal, often ate, compositions. However, the precursor amine TMP(H) is rather expensive so a cheaper substitute would be welcome. Thus this study was aimed towards developing cheaper non‐TMP based mixed‐metal bases and, as cis‐2,6‐dimethylpiperidide (cis‐DMP) was chosen as the alternative amide, developing cis‐DMP zincate chemistry which has received meagre attention compared to that of its methyl‐rich counterpart TMP. A new lithium diethylzincate, [(TMEDA)LiZn(cis‐DMP)Et2] (TMEDA=N,N,N′,N′‐tetramethylethylenediamine) has been synthesised by co‐complexation of Li(cis‐DMP), Et2Zn and TMEDA, and characterised by NMR (including DOSY) spectroscopy and X‐ray crystallography, which revealed a dinuclear contact ion pair arrangement. By using N,N‐diisopropylbenzamide as a test aromatic substrate, the deprotonative reactivity of [(TMEDA)LiZn(cis‐DMP)Et2] has been probed and contrasted with that of the known but previously uninvestigated di‐tert‐butylzincate, [(TMEDA)LiZn(cis‐DMP)tBu2]. The former was found to be the superior base (for example, producing the ortho‐deuteriated product in respective yields of 78 % and 48 % following D2O quenching of zincated benzamide intermediates). An 88 % yield of 2‐iodo‐N,N‐diisopropylbenzamide was obtained on reaction of two equivalents of the diethylzincate with the benzamide followed by iodination. Comparisons are also drawn using 1,1,1,3,3,3‐hexamethyldisilazide (HMDS), diisopropylamide and TMP as the amide component in the lithium amide, Et2Zn and TMEDA system. Under certain conditions, the cis‐DMP base system was found to give improved results in comparison to HMDS and diisopropylamide (DA), and comparable results to a TMP system. Two novel complexes isolated from reactions of the di‐tert‐butylzincate and crystallographically characterised, namely the pre‐metallation complex [{(iPr)2N(Ph)C?O}LiZn(cis‐DMP)tBu2] and the post‐metallation complex [(TMEDA)Li(cis‐DMP){2‐[1‐C(=O)N(iPr)2]C6H4}Zn(tBu)], shed valuable light on the structures and mechanisms involved in these alkali‐metal‐mediated zincation reactions. Aspects of these reactions are also modelled by DFT calculations. 相似文献
992.
Robert K. Pinschmidt Jr. Walter L. Renz W. Eamon Carroll Khalil Yacoub Jennifer Drescher A. F. Nordquist 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):1885-1905
Abstract N-Vinylformamide (NVF, N-ethenylformamide) is a precursor to amide and amine functional polymers and to other monomers, oligomers, and functional polymers. NVF shows attractive physical and toxicological properties and high reactivity, both in polymerization and in subsequent hydrolysis to cationic and reactive amine functional polymers or oligomers. NVF radical polymerization readily yields water soluble homopolymers with molecular weights from 104 to >106. Copolymerizability is similar to other vinyl amides. Unexpectedly, NVF will also undergo cationic oligomerization. Hydrolysis of polymers and copolymers with base or acid is facile, although reactions with neighboring groups (e.g., with coacrylate ester groups to give lactams) complicate copolymer hydrolysis. Reaction of NVF at the unusually acidic NH group allows reaction with isocyanates to give vinylacylureas or Michael addition to acrylates to give a family of new N-vinylformamidopropionate esters. These esters in turn react with functional amines to generate new families of divinyl, vinyl/alcohol functional, or vinyl/amino functional comonomers. Applications for NVF and its derived monomers and polymers appear numerous, in particular in radiation cure coatings, based on their good physical and toxicological properties. 相似文献
993.
Zhe Xu Jared B. Shaw Jennifer S. Brodbelt 《Journal of the American Society for Mass Spectrometry》2013,24(2):265-273
The development of activation/dissociation techniques such as ultraviolet photodissociation (UVPD), infrared multiphoton dissociation (IRMPD), and electron transfer dissociation (ETD) as alternatives to collision induced dissociation (CID) has extended the range of strategies for characterizing biologically relevant molecules. Here, we describe a comprehensive comparison of CID, IRMPD, UVPD, ETD, and hybrid processes termed ETcaD and ET-IRMPD (and analogous hybrid methods in the negative mode NETcaD and NET-IRMPD) for generating sequence-specific fragment ions and allowing adduction sites to be pinpointed for DNA/cisplatin adducts. Among the six MS/MS methods, the numerous products generated by the IRMPD and UVPD techniques resulted in the most specific and extensive backbone cleavages. We conclude that IRMPD and UVPD methods generally offer the best characteristics for pinpointing the cisplatin adduction sites in the fragment-rich spectra. 相似文献
994.
Jennifer K. Angelosante Breia J. Lewis Lisa E. Cooper Rebecca A. Swanson Christopher J. A. Daley 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2263-2272
Herein, two improved synthetic pathways to biologically relevant Cys-Xxx-Cys analogue ligands used in conjunction with metals as metalloenzyme models (Ni for carbon monoxide dehydrogenase/acetyl-CoA synthase A-cluster; Co and Fe for nitrile hydratase) are reported. 相似文献
995.
Luke C. Henderson Megan T. Thornton Nolene Byrne Bronwyn L. Fox Kelsey D. Waugh Jennifer S. Squire Linden Servinis Joshua P. Delaney Hannah L. Brozinski Luke M. Andrighetto Jarrad M. Altimari 《Comptes Rendus Chimie》2013,16(7):634-639
The acid catalysed formation of diphenylmethyl (DPM) thioethers was successfully achieved using the protic ionic liquid (pIL) triethylamine:methanesulfonic acid (TeaMs) as the reaction solvent under microwave irradiation. A slight excess of methanesulfonic acid (10% v/v) was required to facilitate the reaction, which was applied to a variety of thiols. Aliphatic, aromatic and heterocyclic aromatic thiols were converted to their corresponding DPM thioethers in high yields (63–99%), in short reaction times (5–20 min) and using mild temperatures (80–100 °C). Finally, the pIL (TeaMS) was recycled five times without loss of yield. 相似文献
996.
997.
998.
In this article, we examine voluntary oversight programs for nanotechnology in the context of corporate social performance
(CSP) in order to better understand the drivers, barriers, and forms of company participation in such programs. At the theoretical
level, we use the management framework of CSP to understand the voluntary behavior of companies. At the empirical level, we
investigate nanotech industry participation in the Environmental Protection Agency’s Nanoscale Materials Stewardship Program
(NMSP) as an example of CSP, in order to examine the effects of company characteristics on CSP outcomes. The analysis demonstrates
that, on the average, older and larger companies for which nanotech is one of the many business activities demonstrate greater
CSP as judged by company actions, declarations, and self-evaluations. Such companies tended to submit more of the requested
information to the NMSP, including specific information about health and safety, and to claim fewer of the submitted items
as confidential business information. They were also more likely to have on-line statements of generic and nano-specific corporate
social responsibility principles, policies, and achievements. The article suggests a need to encourage smaller and younger
companies to participate in voluntary oversight programs for nanotechnology and presents options for better design of these
programs. 相似文献
999.
Julie Sarama Douglas H. Clements Jeffrey Barrett Douglas W. Van Dine Jennifer S. McDonel 《ZDM》2011,43(5):667-680
Measurement is a critical component of mathematics education, but research on the learning and teaching of measurement is limited, especially compared to topics such as number and operations. To contribute to the establishment of a research base for instruction in measurement, we evaluated and refined a previously developed learning trajectory in early length measurement, focusing on the developmental progressions that provide cognitive accounts of the development of children’s strategic and conceptual knowledge of measure. Findings generally supported the developmental progression, in that children reliably moved through the levels of thinking in that progression. For example, they passed through a level in which they measured length by placing multiple units or attempting to iterate a unit, sometimes leaving gaps between units. However, findings also suggested several refinements to the developmental progression, including the nature and placement of indirect length comparison in the developmental progression and the role of vocabulary, which was an important facilitator of learning for some, but not all, children. 相似文献
1000.
Grebner DM Parks SE Bradley DL Miksis-Olds JL Capone DE Ford JK 《The Journal of the Acoustical Society of America》2011,129(2):1067-1072
Northern resident killer whale pods (Orcinus orca) have distinctive stereotyped pulsed call repertoires that can be used to distinguish groups acoustically. Repertoires are generally stable, with the same call types comprising the repertoire of a given pod over a period of years to decades. Previous studies have shown that some discrete pulsed calls can be subdivided into variants or subtypes. This study suggests that new stereotyped calls may result from the gradual modification of existing call types through subtypes. Vocalizations of individuals and small groups of killer whales were collected using a bottom-mounted hydrophone array in Johnstone Strait, British Columbia in 2006 and 2007. Discriminant analysis of slope variations of a predominant call type, N4, revealed the presence of four distinct call subtypes. Similar to previous studies, there was a divergence of the N4 call between members of different matrilines of the same pod. However, this study reveals that individual killer whales produced multiple subtypes of the N4 call, indicating that divergence in the N4 call is not the result of individual differences, but rather may indicate the gradual evolution of a new stereotyped call. 相似文献