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951.
Determining the modern carbon content of biobased products using radiocarbon analysis 总被引:1,自引:0,他引:1
In support of the USDA Federal Biobased Products Preferred Procurement Program (FB4P), Iowa State University is coordinating testing to determine the "biobased content" of manufactured products. These tests are part of a process to "designate" items that qualify for preferential procurement status with federal agencies. Biobased content determinations are being performed using three radiocarbon dating procedures specified in ASTM D 6866-05. Test results obtained thus far indicate that the AMS and benzene synthesis methods provide comparable results. Data from the CO(2) cocktail method did not agree as well with the data from the other two methods, but were still in reasonably good agreement with those data. Radiocarbon analysis is shown to be a reliable and valuable tool for verifying the biobased content of a wide variety of biobased products. Based on inter- and intra-laboratory comparisons, a reasonable uncertainty to associate with the analyses would be +/-3% (absolute) for the AMS and benzene synthesis methods. Because of limited data availability, additional work is needed to establish the uncertainty of the CO(2) cocktail method for analyzing biobased products. 相似文献
952.
A series of 5-aminosubstituted camptothecin analogs were prepared from the corresponding 5-hydroxycamptothecin using microwave irradiation. The analogs were assayed for ability to inhibit the action of hypoxia inducible factors (HIF-1alpha and HIF-2alpha). The 5-fluoroethyl analog showed potent inhibitory activity and is now the focus of ongoing pathway analysis and potential as an antiproliferative agent. 相似文献
953.
Dominique Bazin Xavier Carpentier Isabelle Brocheriou Peter Dorfmuller Stephane Aubert Christine Chappard Dominique Thiaudire Solenn Reguer Glenn Waychunas Paul Jungers Michel Daudon 《Biochimie》2009,91(10):1294
The role of oligo-elements such as Zn in the genesis of pathological calcifications is widely debated in the literature. An essential element of discussion is given by their localisation either at the surface or within the Ca apatite crystalline network. To determine the localisation, X-ray absorption experiments have been performed at SOLEIL. The Exafs results suggest that Zn atoms, present in the Zn2+ form, are bound to about 4 O atoms at a distance of 2.00 Å, while the interatomic distance RCaO ranges between 2.35 Å and 2.71 Å. Taking into account the content of Zn (around 1000 ppm) and the difference in ionic radius between Zn2+ (0.074 nm) and Ca2+ (0.099 nm), a significant longer interatomic distance would be expected in the case of Zn replacing Ca within the apatite crystalline network. We thus conclude that Zn atoms are localised at the surface and not in the apatite nanocrystal structure. Such structural result has essential biological implications for at least two reasons. Some oligoelements have a marked effect on the transformation of chemical phases, and may modify the morphology of crystals. These are both major issues because, in the case of kidney stones, the medical treatment depends strongly on the precise chemical phase and on the morphology of the biological entities at both macroscopic and mesoscopic scales. 相似文献
954.
The mistyping of the angiotensin I-converting enzyme insertion/deletion (ACE I/D) has been well documented, and new methods have been suggested here to improve the genotyping efficiency. Buccal cell
samples were collected from 157 young Caucasians, and genotyped using previously known and newly developed PCR amplification
genotyping techniques, as well as PCR-RFLP tests for three single nucleotide polymorphisms (rs4327, rs4341 and rs4343). Inconsistent
genotyping results were found when using only the PCR amplification genotyping techniques across repeated attempts (8% to
45%), however, individual SNP genotyping was highly consistent (100%). Two SNPs (rs4341 and rs4343) were in complete LD and
SNP rs4327 was in high LD with the ACE I/D. The ACE I/D was in HW equilibrium in the portion of the population with consistent genotyping results, whereas the three SNPs were
not in HW equilibrium. The mistyping of ACE I/D by only PCR amplification can be improved using alternative methods. 相似文献
955.
Glenn J. Lurman Christian H. Bock Hans-O. Poertner 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2009,179(5):623-633
Thermal acclimation is frequently cited as a means by which ectothermic animals improve their Darwinian fitness, i.e. the
beneficial acclimation hypothesis. As the critical swimming speed (U
crit) test is often used as a proxy measure of fitness, we acclimated Atlantic cod (Gadus morhua) to 4 and 10°C and then assessed their U
crit swimming performance at their respective acclimation temperatures and during acute temperature reversal. Because phenotypic
differences exist between different populations of cod, we undertook these experiments in two different populations, North
Sea cod and North East Arctic cod. Acclimation to 4 or 10°C had a minimal effect on swimming performance or U
crit, however test temperature did, with all groups having a 10–17% higher U
crit at 10°C. The swimming efficiency was significantly lower in all groups at 4°C arguably due to the compression of the muscle
fibre recruitment order. This also led to a reduction in the duration of “kick and glide” swimming at 4°C. No significant
differences were seen between the two populations in any of the measured parameters, due possibly to the extended acclimation
period. Our data indicate that acclimation imparts little benefit on U
crit swimming test in Atlantic cod. Further efforts need to identify the functional consequences of the long-term thermal acclimation
process. 相似文献
956.
Glenn P. Johnson Luis Petersen Alfred D. French Peter J. Reilly 《Carbohydrate research》2009,344(16):2157-2166
Patterns of scissile bond twisting have been found in crystal structures of glycoside hydrolases (GHs) that are complexed with substrates and inhibitors. To estimate the increased potential energy in the substrates that results from this twisting, we have plotted torsion angles for the scissile bonds on hybrid Quantum Mechanics::Molecular Mechanics energy surfaces. Eight such maps were constructed, including one for α-maltose and three for different forms of methyl α-acarviosinide to provide energies for twisting of α-(1,4) glycosidic bonds. Maps were also made for β-thiocellobiose and for three β-cellobiose conformers having different glycon ring shapes to model distortions of β-(1,4) glycosidic bonds. Different GH families twist scissile glycosidic bonds differently, increasing their potential energies from 0.5 to 9.5 kcal/mol. In general, the direction of twisting of the glycosidic bond away from the conformation of lowest intramolecular energy correlates with the position (syn or anti) of the proton donor with respect to the glycon’s ring oxygen atom. This correlation suggests that glycosidic bond distortion is important for the optimal orientation of one of the glycosidic oxygen lone pairs toward the enzyme’s proton donor. 相似文献
957.
Ryan M. Anderson Justin A. Bosch Mary G. Goll Daniel Hesselson P. Duc Si Dong Donghun Shin Neil C. Chi Chong Hyun Shin Amnon Schlegel Marnie Halpern Didier Y.R. Stainier 《Developmental biology》2009,334(1):213-223
Developmental mechanisms regulating gene expression and the stable acquisition of cell fate direct cytodifferentiation during organogenesis. Moreover, it is likely that such mechanisms could be exploited to repair or regenerate damaged organs. DNA methyltransferases (Dnmts) are enzymes critical for epigenetic regulation, and are used in concert with histone methylation and acetylation to regulate gene expression and maintain genomic integrity and chromosome structure. We carried out two forward genetic screens for regulators of endodermal organ development. In the first, we screened for altered morphology of developing digestive organs, while in the second we screed for the lack of terminally differentiated cell types in the pancreas and liver. From these screens, we identified two mutant alleles of zebrafish dnmt1. Both lesions are predicted to eliminate dnmt1 function; one is a missense mutation in the catalytic domain and the other is a nonsense mutation that eliminates the catalytic domain. In zebrafish dnmt1 mutants, the pancreas and liver form normally, but begin to degenerate after 84 h post fertilization (hpf). Acinar cells are nearly abolished through apoptosis by 100 hpf, though neither DNA replication, nor entry into mitosis is halted in the absence of detectable Dnmt1. However, endocrine cells and ducts are largely spared. Surprisingly, dnmt1 mutants and dnmt1 morpholino-injected larvae show increased capacity for pancreatic beta cell regeneration in an inducible model of pancreatic beta cell ablation. Thus, our data suggest that Dnmt1 is dispensable for pancreatic duct or endocrine cell formation, but not for acinar cell survival. In addition, Dnmt1 may influence the differentiation of pancreatic beta cell progenitors or the reprogramming of cells toward the pancreatic beta cell fate. 相似文献
958.
Chris Wiley Anna Qvarnström Gunilla Andersson Thomas Borge Glenn‐Peter Sætre 《Evolution; international journal of organic evolution》2009,63(7):1731-1739
Understanding speciation depends on an accurate assessment of the reproductive barriers separating newly diverged populations. In several taxonomic groups, prezygotic barriers, especially preferences for conspecific mates, are thought to play the dominant role in speciation. However, the importance of postzygotic barriers (i.e., low fitness of hybrid offspring) may be widely underestimated. In this study, we examined how well the widely used proxy of postzygotic isolation (reproductive output of F1 hybrids) reflects the long‐term fitness consequences of hybridization between two closely related species of birds. Using 40 species‐specific single nucleotide polymorphism (SNP) markers, we genotyped a mixed population of collared and pied flycatchers (Ficedula albicollis and F. hypoleuca) to identify grand‐ and great grand‐offspring from interspecific crosses to derive an accurate, multigeneration estimate of postzygotic isolation. Two independent estimates of fitness show that hybridization results in 2.4% and 2.7% of the number of descendents typical of conspecific pairing. This postzygotic isolation was considerably stronger than estimates based on F1 hybrids. Our results demonstrate that, in nature, combined selection against hybrids and backcrossed individuals may result in almost complete postzygotic isolation between two comparatively young species. If these findings are general, postzygotic barriers separating hybridizing populations may be much stronger than previously thought. 相似文献
959.
960.