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151.
Campylobacter jejuni adenosine triphosphate phosphoribosyltransferase is an active hexamer that is allosterically controlled by the twisting of a regulatory tail 下载免费PDF全文
Gerd Mittelstädt Gert‐Jan Moggré Santosh Panjikar Ali Reza Nazmi Emily J. Parker 《Protein science : a publication of the Protein Society》2016,25(8):1492-1506
Adenosine triphosphate phosphoribosyltransferase (ATP‐PRT) catalyzes the first committed step of the histidine biosynthesis in plants and microorganisms. Here, we present the functional and structural characterization of the ATP‐PRT from the pathogenic ε‐proteobacteria Campylobacter jejuni (CjeATP‐PRT). This enzyme is a member of the long form (HisGL) ATP‐PRT and is allosterically inhibited by histidine, which binds to a remote regulatory domain, and competitively inhibited by AMP. In the crystalline form, CjeATP‐PRT was found to adopt two distinctly different hexameric conformations, with an open homohexameric structure observed in the presence of substrate ATP, and a more compact closed form present when inhibitor histidine is bound. CjeATP‐PRT was observed to adopt only a hexameric quaternary structure in solution, contradicting previous hypotheses favoring an allosteric mechanism driven by an oligomer equilibrium. Instead, this study supports the conclusion that the ATP‐PRT long form hexamer is the active species; the tightening of this structure in response to remote histidine binding results in an inhibited enzyme. 相似文献
152.
We have generated new sensors for the specific detection and studies of bioavailability of metals by engineering Pseudomonas fluorescens with reporter gene systems. One broad host range mercury (pTPT11) and two arsenite (pTPT21 and pTPT31) sensor plasmids that
express metal presence by luminescence phenotype were constructed and transferred into Escherichia coli DH5α and Pseudomonas fluorescens OS8. The maximal induction was reached after 2 h of incubation in metal solutions at room temperature (22°C). In optimized
conditions the half maximal velocity of reaction was achieved at acidic pH using a d-luciferin substrate concentration that was nearly sixfold lower for P. fluorescens OS8 than for E. coli DH5α. When using a luciferin concentration (150 μM) that was optimal for E. coli the luminescence declined rapidly in the case of Pseudomonas, for which the substrate level 25 μM gave a stable reading between about 20 min and 3 h. The ability of the strain OS8 to
quantitatively detect specific heavy metals in spiked soil and soil extracts is as good, or even better in being a real-time
reporter system, than that of a traditional chemical analysis. The Pseudomonas strain used is an isolate from pine rhizosphere in oil and heavy metal contaminated soil. It is also a good humus soil colonizer
and is therefore a good candidate for measuring soil heavy metal bioavailability. 相似文献
153.
154.
Leena Peltonen Piritta Koistinen Milja Karjalainen Antti Häkkinen Jouni Hirvonen 《AAPS PharmSciTech》2002,3(4):52-58
The aim of this study was to formulate nanoparticles from poly(I)lactide by a modified nanoprecipitation method. The main
focus was to study the effect of cosolvent selection on the shape, size, formation efficiency, degree of crystallinity, x-ray
diffraction (XRD) reflection pattern, and zeta potential value of the particles. Low-molecular-weight (2000 g/mol) poly(I)lactide
was used as a polymer, and sodium cromoglycate was used as a drug. Acetone, ethanol, and methanol were selected as cosolvents.
Optimal nanoparticles were achieved with ethanol as a cosolvent, and the formation efficiency of the particles was also higher
with ethanol as compared with acetone or methanol. The particles formulated by ethanol and acetone appeared round and smooth,
while with methanol they were slightly angular. When the volume of the inner phase was decreased during the nanoprecipitation
process, the mean particle size was also decreased with all the solvents, but the particles were more prone to aggregate.
The XRD reflection pattern and the degree of crystallinity were more dependent were more prone to aggregate. The XRD reflection
pattern and the degree of crystallinity were more dependent on the amount of the solvents in the inner phase than on the properties
of the individual cosolvents. The zeta potential values of all the particle batches were slightly negative, which partially
explains the increased tendency toward particle aggregation. 相似文献
155.
Nest-mate recognition template of guard honeybees (Apis mellifera) is modified by wax comb transfer 下载免费PDF全文
Couvillon MJ Caple JP Endsor SL Kärcher M Russell TE Storey DE Ratnieks FL 《Biology letters》2007,3(3):228-230
In recognition, discriminators use sensory information to make decisions. For example, honeybee (Apis mellifera) entrance guards discriminate between nest-mates and intruders by comparing their odours with a template of the colony odour. Comb wax plays a major role in honeybee recognition. We measured the rejection rates of nest-mate and non-nest-mate worker bees by entrance guards before and after a unidirectional transfer of wax comb from a 'comb donor' hive to a 'comb receiver' hive. Our results showed a significant effect that occurred in one direction. Guards in the comb receiver hive became more accepting of non-nest-mates from the comb donor hive (rejection decreased from 70 to 47%); however, guards in the comb donor hive did not become more accepting of bees from the comb receiver hive. These data strongly support the hypothesis that the transfer of wax comb increases the acceptance of non-nest-mates not by changing the odour of the bees, but by changing the template used by guards. 相似文献
156.
Mäe M Myrberg H Jiang Y Paves H Valkna A Langel U 《Biochimica et biophysica acta》2005,1669(2):101-107
Cells are protected from the surrounding environment by plasma membrane which is impenetrable for most hydrophilic molecules. In the last 10 years cell-penetrating peptides (CPPs) have been discovered and developed. CPPs enter mammalian cells and carry cargo molecules over the plasma membrane with a molecular weight several times their own. Known transformation methods for plant cells have relatively low efficiency and require improvement. The possibility to use CPPs as potential delivery vectors for internalisation in plant cells has been studied in the present work. We analyse and compare the uptake of the fluorescein-labeled CPPs, transportan, TP10, penetratin and pVEC in Bowes human melanoma cells and Nicotiana tabacum cultivar (cv.) SR-1 protoplasts (plant cells without cell wall). We study the internalisation efficiency of CPPs with fluorescence microscopy, spectrofluorometry and fluorescence-activated cell sorter (FACS). All methods indicate, for the first time, that these CPPs can internalise into N. tabacum cv. SR-1 protoplasts. Transportan has the highest uptake efficacy among the studied peptides, both in mammalian cells and plant protoplast. The internalisation of CPPs by plant protoplasts may open up a new effective method for transfection in plants. 相似文献
157.
Parameters affecting the fermentative lactic acid (LA) production are summarized and discussed: microorganism, carbon- and nitrogen-source, fermentation mode, pH, and temperature. LA production is compared in terms of LA concentration, LA yield and LA productivity. Also by-product formation and LA isomery are discussed. 相似文献
158.
Erna Suutari Jukka Salmela Lauri Paasivirta Markus J. Rantala Katja Tynkkynen Mari Luojumäki Jukka Suhonen 《Journal of Insect Conservation》2009,13(4):413-419
Species with narrow ranges and specialised traits are most at risk, and the extinction wave is further enhanced by coextinctions.
We studied the conservation value and indicator potential of Stratiotes aloides, an aquatic macrophyte that has declined considerably in Europe. Our purpose was to determine whether S. aloides could be used as an indicator of a valuable habitat in terms of macroarthropod diversity and species richness. The potential
occurrence of an internationally endangered Stratiotes-habitat specialist, the dragonfly Aeshna viridis, can increase the conservation value of plant colonies. S. aloides beds harboured diverse macroarthropod fauna often containing species of conservation concern, including A. viridis. Stratiotes is a potential indicator of a valuable habitat, and its indicator value is enhanced by the easy identification of the species.
However, its use as an indicator of a defined macroarthropod community is limited because no particular community type is
connected to it. We suggest that protecting Stratiotes simultaneously conserves valuable arthropod fauna, including A. viridis. 相似文献
159.
Conditioned medium (CM) taken from a serum-free culture of Trichoplusia ni (BTI-Tn-5B1-4, High Five) cells on days 2 and 3, shortened the lagphase and increased the maximum cell density when added to T. ni cultures with low-inoculum cell density. Gel filtration fractions of CM, eluting at around 45kDa, stimulated cell proliferation even better than CM. A protein in the gel filtration fraction was identified by N-terminal amino acid sequencing as a proteinase, related to a snake venom metalloproteinase. Casein zymography showed, multiple metalloproteinase bands between 48 and 25kDa, as well as precursor forms above 48kDa. Metalloproteinase bands below the main band at 48kDa were autocatalytic degradation products. Metalloproteinase activity was the sole factor responsible for the growth stimulating effect of CM as shown by using the specific metalloproteinase inhibitor dl-thiorphan. Metalloproteinases have recently been shown to release growth factors from sequestering extracellular proteins. We propose that the metalloproteinase is involved in autocrine regulation of T. ni proliferation in serum-free media. In addition, a gel filtration fraction of CM, eluting at about 10kDa, inhibited cell growth. Apart from a lysozyme precursor protein and a cyclophilin-like protein, a kazal-type proteinase inhibitor could be identified in this fraction. 相似文献
160.
Insect workers can increase their inclusive fitness by biasing colony sex allocation towards males when their mother queen is mated to multiple males and females when she is singly mated. Workers need heritable variation in odour diversity to assess queen mating frequency. Here we present a simple one-locus two-allele model, which shows that the sex ratio specialization itself will often select against rare alleles that would provide additional information for the assessment of queen mating frequency. However, under certain rather restricted conditions, such as when sex ratios are highly female biased, and when worker reproduction is rare, sex ratio specialization can select for rare alleles. This suggests that sex allocation biasing by workers will usually reduce the very information that workers need to assess queen mating frequency. Our model is an example where an explicit treatment of underlying genetics and mechanisms of behaviour, such as information use, is necessary to fully understand the evolution of an adaptive behavioural strategy. 相似文献