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121.
We advocate the concept of an arbuscular mycorrhiza (AM) as a temporally and spatially complex symbiosis representing a suite
of hosts and fungi, as against the more traditional "dual organism" view. We use the hierarchical framework presented in Fig. 1
as a basis for organizing many unanswered questions, and several questions that have not been asked, concerning the role of
AM in responses to elevated atmospheric CO2. We include the following levels: plant host, plant population, plant community, functional group and ecosystem. Measurements
of the contributions of AM fungi at the various levels require the use of different response variables. For example, hyphal
nutrient translocation rates or percent AM root infection may be important measures at the individual plant level, but hyphal
biomass or glomalin production and turnover are more relevant at the ecosystem level. There is a discrepancy between our knowledge
of the multifaceted role of AM fungi in plant and ecosystem ecology and most of the current research aimed at elucidating
the importance of this symbiosis in global-change scenarios. Our framework for more integrated and multifactorial research
on mycorrhizal involvement in regulating CO2 responses may also serve to enhance communication between researchers working at different scales on large global-change
ecosystem projects.
Accepted: 12 February 1999 相似文献
122.
Craig R. Allen 《Biological invasions》2006,8(3):491-500
Biological invasions are an increasing global challenge, for which single-species studies and analyses focused on testing
single hypotheses of causation in isolation are unlikely to provide much additional insight. Species interact with other species
to create communities, which derive from species interactions and from the interactions of species with the scale specific
elements of the landscape that provide suitable habitat and exploitable resources. I used logistic regression analysis to
sort among potential intrinsic, community and landscape variables that theoretically influence introduction success. I utilized
the avian fauna of the Everglades of South Florida, and the variables body mass, distance to nearest neighbor (in terms of
body mass), year of introduction, presence of congeners, guild membership, continent of origin, distribution in a body mass
aggregation or gap, and distance to body-mass aggregation edge (in terms of body mass). Two variables were significant predictors
of introduction success. Introduced avian species whose body mass placed them nearer to a body-mass aggregation edge and further
from their neighbor were more likely to become successfully established. This suggests that community interactions, and community
level phenomena, may be better understood by explicitly incorporating scale. 相似文献
123.
Indest T Laine J Ribitsch V Johansson LS Stana-Kleinschek K Strnad S 《Biomacromolecules》2008,9(8):2207-2214
The adsorption behavior of chitosan on poly(ethylene terephthalate) (PET) model film surface was studied using the quartz crystal microbalance (QCM) technique. QCM with a dissipation unit (QCM-D) represents a very sensitive technique for adsorption studies at the solid/liquid interface in situ, with capability of detecting a submonolayer of adsorbate on the quartz crystal surface. Chitosan as well as PET were chosen for this study due to their promising biocompatible properties and numerous possibilities to be used in biomedical applications. As a first step, PET foils were activated by alkaline hydrolysis in order to increase their hydrophilicity. Model thin films were prepared from PET foils by the spin coating technique. The chemical composition of the obtained model PET films was analyzed using X-ray photoelectron spectroscopy (XPS) and their morphology was characterized by atomic force microscopy (AFM). Furthermore, the adsorption behavior of chitosan on these activated PET films and the influence of adsorption parameters (pH, ionic strength and chitosan solution concentration) were investigated in detail. Additionally, the surface chemistry and morphology of the PET films and the chitosan coated PET films were analyzed with XPS and AFM. 相似文献
124.
Effect of hemicellulose and lignin removal on enzymatic hydrolysis of steam pretreated corn stover 总被引:12,自引:0,他引:12
Ethanol can be produced from lignocellulosic biomass using steam pretreatment followed by enzymatic hydrolysis and fermentation. The sugar yields, from both hemicellulose and cellulose are critical parameters for an economically-feasible ethanol production process. This study shows that a near-theoretical glucose yield (96-104%) from acid-catalysed steam pretreated corn stover can be obtained if xylanases are used to supplement cellulases during hydrolysis. Xylanases hydrolyse residual hemicellulose, thereby improving the access of enzymes to cellulose. Under these conditions, xylose yields reached 70-74%. When pre-treatment severity was reduced by using autocatalysis instead of acid-catalysed steam pretreatment, xylose yields were increased to 80-86%. Partial delignification of pretreated material was also evaluated as a way to increase the overall sugar yield. The overall glucose yield increased slightly due to delignification but the overall xylose yield decreased due to hemicellulose loss in the delignification step. The data also demonstrate that steam pretreatment is a robust process: corn stover from Europe and North America showed only minor differences in behaviour. 相似文献
125.
126.
Cloning and analysis of DNA sequences from Streptomyces hygroscopicus encoding geldanamycin biosynthesis 总被引:1,自引:0,他引:1
A gene library constructed from large (20 kb) fragments of total DNA from the geldananmycin-producing strain Streptomyces hygroscopicus 3602 cloned in the plasmid vector pIJ61 were used to transform S. lividans TK24. Three transformants of about 800 tested were found to have acquired the ability to produce an antibiotic lethal to a geldanamycin-sensitive strain of Bacillus subtilis. The plasmids isolated from these transformants, pIA101, pIA102 and pIA103, each contained an insert of 15 kb. A 4.5 kb DNA fragment from the insert in pIA102 hybridised to DNA from S. hygroscopicus 3602 and to DNA encoding part of the erythromycin polyketide synthase but not to S. lividans TK24 DNA. The integration-defective phage vector C31 KC515 containing this 4.5 kb fragment was able to lysogenise S. hygroscopicus 3602 to produce lysogens defective in geldanamycin production. Loss of the prophage restored the ability to produce geldanamycin. Extracts of fermentation broth cultures of S. lividans containing pIA101, pIA102 and pIA102 and pIA103 analysed by thin-layer chromatography (TLC) contained compounds identical or very similar to purified geldanamycin, which were not present in S. lividans. These compounds showed a mass spectrum indistinguishable from geldanamycin. The evidence suggests that the clones contain DNA sequences encoding functions required for geldanamycin biosynthesis including components of the polyketide synthase. 相似文献
127.
Type V collagen as the target for type-3 fimbriae, enterobacterial adherence organelles 总被引:22,自引:2,他引:22
A.-M. Tarkkanen B. L. Allen B. Westerlund H. Holthöfer P. Kuusela L. Risteli S. Clegg T. K. Korhonen 《Molecular microbiology》1990,4(8):1353-1361
Tissue-binding specificity of the type-3 fimbriae of pathogenic enteric bacteria was determined using frozen sections of human kidney. A wild-type Klebsiella sp. strain and the recombinant strain Escherichia coli HB101(pFK12), both expressing type-3 fimbriae, as well as the purified type-3 fimbriae effectively bound to sites at or adjacent to tubular basement membranes, Bowman's capsule, arterial walls, and the interstitial connective tissue. Bacterial adherence to kidney was decreased after collagenase treatment of the tissue sections. Recombinant strains expressing type-3 fimbriae specifically adhered to type V collagen immobilized on glass slides, whereas other collagens, fibronectin or laminin did not support bacterial adherence. In accordance with these findings, specific binding of purified type-3 fimbriae to immobilized type V collagen was demonstrated. Specific adhesion to type V collagen was also seen with the recombinant strain HB101(pFK52/pDC17), which expresses the mrkD gene of the type-3 fimbrial gene cluster in association with the pap-encoded fimbrial filament of E. coli, showing that the observed binding was mediated by the minor lectin (MrkD) protein of the type-3 fimbrial filament. The interaction is highly dependent on the conformation of type V collagen molecules since type V collagen in solution did not react with the fimbriae. Specific binding to type V collagen was also exhibited by type-3 fimbriate strains of Yersinia and Salmonella, showing that the ability to use type V collagen as tissue target is widespread among enteric bacteria. 相似文献
128.
In the search among biological particles for a standard for counting human platelets, a strain of Absidia corymbifera was found to have spores that resembled platelets. After fixing in formalin and autoclaving the spores had a similar mean cell volume to that of human platelets. A suspension of these killed spores was tested in 100 laboratories and gave consistent results as a standard for human platelet counting. The Absidia corymbifera standard can be used in electronic counting methods but not in sedimentation methods, as the spores will be removed by centrifugation. 相似文献
129.
130.
H J Allen M Cywinski R Palmberg R A DiCioccio 《Archives of biochemistry and biophysics》1987,256(2):523-533
Galactoside-inhibitable lectins have been isolated from rabbit, rat, mouse, pig, lamb, calf, and human spleens. Native molecular mass, subunit structure, pI, and hemagglutinating activity have been compared for these lectins. The yields of lectin varied from 1.8 mg/kg for rabbit spleen to 79 mg/kg for lamb spleen. Pig, lamb, calf, and human spleen lectins yielded single protein peaks when subjected to Superose 12 fast-protein liquid chromatography. The apparent molecular mass for these lectins was 33-34 kDa. In contrast, rat and mouse spleen lectin preparations were separated into three components ranging from 8.4 to 34 kDa. Superose 12 chromatography of rabbit spleen lectin revealed the presence of at least six components. Gradient slab gel sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed the presence of single polypeptides for pig, calf, lamb, and human lectins corresponding to a molecular mass of 14-14.5 kDa. Multiple polypeptides were detected for the mouse, rat, and rabbit lectins. The molecular mass of the major polypeptides were 15, 15, and 17 kDa for rat, mouse, and rabbit, respectively. The presence of isolectins in all preparations was shown by isoelectric focusing. The major isolectins were acidic proteins with pI 4.38-4.80. Hemagglutination and hemagglutination inhibition assays demonstrated similarities as well as differences among the lectin preparations. Hemagglutinating activity could not be demonstrated in rabbit spleen extracts nor for isolated putative lectin. Human buffy coat cells were reversibly agglutinated by calf and human spleen lectins, demonstrating the presence of leucocyte cell surface lectin receptors. 相似文献