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111.
Joseph L. Hughes Nicholas Cox A. William Rutherford Elmars Krausz Alain Boussac 《BBA》2010,1797(1):11-6021
In Photosystem II (PSII) from Thermosynechococcus elongatus, high-light intensity growth conditions induce the preferential expression of the psbA3 gene over the psbA1 gene. These genes encode for the D1 protein variants labeled D1:3 and D1:1, respectively. We have compared steady state absorption and photo-induced difference spectra at < 10 K of PSII containing either D1:1 or D1:3. The following differences were observed. (i) The pheophytin Qx band was red-shifted in D1:3 (547.3 nm) compared to D1:1 (544.3 nm). (ii) The electrochromism on the PheoD1 Qx band induced by QA− (the C550 shift) was more asymmetric in D1:3. (iii) The two variants differed in their responses to excitation with far red (704 nm) light. When green light was used there was little difference between the two variants. With far red light the stable (t1/2 > 50 ms) QA− yield was ∼ 95% in D1:3, and ∼ 60% in D1:1, relative to green light excitation. (iv) For the D1:1 variant, the quantum efficiency of photo-induced oxidation of side-pathway donors was lower. These effects can be correlated with amino acid changes between the two D1 variants. The effects on the pheophytin Qx band can be attributed to the hydrogen bond from Glu130 in D1:3 to the 131-keto of PheoD1, which is absent for Gln130 in D1:1. The reduced yield with red light in the D1:1 variant could be associated with either the Glu130Gln change, and/or the four changes near the binding site of PD1, in particular Ser153Ala. Photo-induced QA− formation with far red light is assigned to the direct optical excitation of a weakly absorbing charge transfer state of the reaction centre. We suggest that this state is blue-shifted in the D1:1 variant. A reduced efficiency for the oxidation of side-pathway donors in the D1:1 variant could be explained by a variation in the location and/or redox potential of P+. 相似文献
112.
目的:探讨干燥综合征累及中枢神经病变的临床表现及诊断、鉴别诊断、治疗。方法:报告中国人民解放军第175医院1例累及中枢神经病变的干燥综合征患者的临床资料并复习相关文献,对其临床表现、诊断、容易混淆的鉴别诊断及治疗进行分析。结果:1例累及中枢神经病变的干燥综合征患者经治疗病情好转出院。结论:累及中枢神经病变的干燥综合征,尤其以中枢神经系统症状为首发表现者,极易误诊为多发性硬化,遇可疑病例应及时完善检查,避免因忽视其它系统症状而导致漏诊和误诊,影响患者的预后。 相似文献
113.
Liu Y 《Mathematical biosciences》2007,208(1):193-204
In this paper, we study the existence of cycles in a predator-prey system in which the prey species is equipped with the group defense capability. Some geometric criteria are developed, relating the location of the two positive equilibria on the prey isocline and the non-existence of cycles. We show that under a general geometric condition, if both positive equilibria lie on a downslope or both lie on an upslope of the prey isocline, cycles do not exist. 相似文献
114.
Herbivores influence nutrient cycling and primary production in terrestrial plant communities. However, both empirical and
theoretical studies have indicated that the mechanisms by which herbivores influence nutrient availability, and thus their
net effects on primary production, might differ between time scales. For a grassland in southeast England, we show that the
effects of rabbits on primary production change over time in a set of grazed plots paired with exclosures ranging from 0 to
14 years in age. Herbivore exclusion decreased net aboveground primary production (APP) in the short term, but increased APP
in the long term. APP was closely correlated with N mineralization rates in both grazed and ungrazed treatments, and accumulation
of litter within the grazing exclosures led to higher N mineralization rates in exclosures in the long run. Rabbit grazing
did not influence litter quality. The low contrast in palatability between species and the presence of grazing-tolerant plants
might prevent rabbits from favoring unpalatable plant species that decompose slowly, in contrast to results from other ecosystems.
Our results indicate that it is essential to understand the effects on N cycling in order to predict the effect of rabbit
grazing on APP. Rabbits might decrease N mineralization and APP in the long term by increasing losses of N from grasslands. 相似文献
115.
Alcohol dehydrogenase (ADH) is a key enzyme in the production and utilization of alcohols. Some also catalyze the formation
of carboxylate esters from alcohols and aldehydes. The ADH1 and ADH3 genes of Neurospora crassa FGSC2489 were cloned and expressed in recombinant Escherichia coli to investigate their alcohol dehydrogenation and carboxylate ester formation abilities. Homology analysis and sequence alignment
of amino acid sequence indicated that ADH1 and ADH3 of N. crassa contained a zinc-binding consensus sequence and a NAD+-binding motif and showed 54–75% identity with fungi ADHs. N. crassa ADH1 was expressed in E. coli to give a specific activity of 289 ± 9 mU/mg using ethanol and NAD+ as substrate and cofactor, respectively. Corresponding experiments on the expression and activity of ADH3 gave 4 mU/mg of specific activity. N. crassa
ADH1 preferred primary alcohols containing C3–C8 carbons to secondary alcohols such as 2-propanol and 2-butanol. N. crassa
ADH1 possessed 5.3 mU/mg of specific carboxylate ester-forming activity accumulating 0.4 mM of ethyl acetate in 18 h. Substrate
specificity of various linear alcohols and aldehydes indicated that short chain-length alcohols and aldehydes were good substrates
for carboxylate ester production. N. crassa
ADH1 was a primary alcohol dehydrogenase using cofactor NAD+ preferably and possessed carboxylate ester-forming activity with short chain alcohols and aldehydes. 相似文献
116.
117.
Photosynthetic efficiency as a function of thermal stratification and phytoplankton size structure in an oligotrophic alpine lake 总被引:4,自引:2,他引:2
Christina Kaiblinger Sonja Greisberger Katrin Teubner Martin T. Dokulil 《Hydrobiologia》2007,578(1):29-36
Allometric relationships of phytoplankton communities were studied on the basis of a five-year data-set in a deep oligotrophic
alpine lake in Austria. The seasonal phytoplankton succession in Mondsee is characterised by diatoms during winter mixing
and a distinct metalimnetic population of Planktothrix rubescens during stratification in summer. The variation of phytoplankton photosynthetic efficiency between seasons was assessed using
in situ carbon-uptake rates (5 years data) and Fast Repetition Rate Fluorometry (FRRF) (2 years data). The light-saturated,
chlorophyll-specific rate of photosynthesis (P*max), irradiance at the onset of saturation (E
k) and maximum light-utilisation efficiency (α*) were determined for winter mixing and summer stratification. Fluorescence-based parameters as the functional absorption
cross section of Photosystem II (σ
PSII) and the photochemical quantum yield (F
v/F
m) were additionally analysed in 2003 and 2004 to study the underlying physiological mechanisms for the variability in photosynthetic
performance. Beyond their sensitivity to changing environmental conditions like thermal stratification, phytoplankton populations
differ in their photosynthetic behaviour according to their size structure. Therefore Photosynthesis vs. Irradiance (P/E)-relationships
were analysed in detail within a 1-year period from size fractionated cell counts, chlorophyll-a and carbon-uptake. 相似文献
118.
We used three isolated clusters of small ephemeral rock pools on a sandstone flat in Utah to test the importance of local
structuring processes on aquatic invertebrate communities. In the three clusters we characterized all ephemeral rock pools
(total: 27) for their morphometry, and monitored their water quality, hydrology and community assemblage during a full hydrocycle.
In each cluster we also sampled a set of more permanent interconnected freshwater systems positioned in a wash, draining the
water from each cluster of rock pools. This design allowed additional testing for the potential role of more permanent water
bodies in the region as source populations for the active dispersers and the effect on the community structure in the rock
pools. Species richness and community composition in the rock pools correlated with level of permanence and the ammonia concentration.
The length of the rock pool inundation cycle shaped community structure, most probably by inhibiting colonization by some
taxa (e.g. tadpoles and insect larvae) through developmental constraints. The gradient in ammonia concentrations probably
reflects differences in primary production. The more permanent water bodies in each wash differed both environmentally and
in community composition from the connected set of rock pools. A limited set of active dispersers was observed in the rock
pools. Our findings indicate that aquatic invertebrate communities in the ephemeral rock pools are mainly structured through
habitat permanence, possibly linked with biotic interactions and primary production.
Handling editor: S. I. Dodson 相似文献
119.
Knott ML Matthaei KI Giacomin PR Wang H Foster PS Dent LA 《International journal for parasitology》2007,37(12):1367-1378
Eosinophils are an important feature of immune responses to infections with many of the tissue-invasive helminth parasites. The cytokine IL-5 and a high-affinity double GATA-binding site within the GATA-1 promoter are critical for eosinophilopoiesis. In this study, we believe we demonstrate for the first time that defects in eosinophilopoiesis are associated with impaired resistance to Nippostrongylus brasiliensis. Primary and secondary infections were established in wildtype (WT), IL-5(-/-) and DeltadblGATA mice. Resistance to secondary infections was impaired in IL-5(-/-) and DeltadblGATA mice, with significantly more larvae able to reach the lungs 2 days p.i. Pulmonary inflammation was minimal in all strains in the first 2 days of both primary and secondary infections, suggesting that eosinophil-dependent resistance occurred before larvae reached this site. Intestinal worm burdens and/or parasite egg production in primary infections were greater in animals with defective eosinophilopoiesis. While larvae did reach the gut by day 3 of secondary infections of WT and IL-5(-/-) mice, worms were expelled by day 7, even in the complete absence of eosinophils in tissues of the small intestine. This and our previous studies indicate that N. brasiliensis are likely to be exquisitely sensitive to attack by eosinophils soon after entry into the skin. Eosinophils in the gut may make a modest contribution to resistance on first exposure to the parasite, but are not required for expulsion in either primary or secondary infections. In order to mount an effective immune response it may be vital for the host to identify and attack the parasite before it implements immune evasion strategies and migrates to other anatomical sites. These observations may be of particular significance for the development of successful vaccines against hookworms and other nematodes. 相似文献
120.
乳鼠成骨细胞体外培养 总被引:2,自引:0,他引:2
目的建立乳鼠成骨细胞体外培养方法,探讨该方法的可行性和应用价值。方法用出生1~3 d乳鼠颅骨,采用多次胶原酶消化法进行细胞体外培养。倒置显微镜观察细胞形态,对其碱性磷酸酶(ALP)活性及矿化能力进行鉴定,并测定细胞生长曲线。结果原代培养24 h后,大量细胞贴壁生长,细胞呈圆形,48 h后,贴壁细胞呈长梭形、三角形或不规则多边形,并且贴壁细胞伸出2~3个突起,胞质透亮、饱满,7 d后细胞铺满整个平皿底面。经鉴定,培养细胞具有体内成骨细胞的生物学特性。细胞接种后第1与第2个24 h为细胞的潜伏适应期,第3与第7个24 h生长曲线基本为线性曲线,是细胞的对数生长期。结论采用胶原酶消化法分离培养成骨细胞的方法切实可行。 相似文献