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991.
Human activities have greatly increased the input of biologically available nitrogen (N) from land-based sources to aquatic
ecosystems; yet few studies have examined how human actions influence N export in regions with a strong seasonality in water
availability. In this study, we quantified N inputs and outputs for 23 California watersheds and examined how climate, hydrology,
and land use practices influenced watershed N export. N inputs ranged from 581 to 11,234 kg N km−2 year−1 among watersheds, with 80% of total input for the region originating from agriculture (inorganic fertilizer, manure, and
legumes). Of the potential N sources examined, mean annual concentrations of dissolved organic N and dissolved inorganic N
in study rivers correlated most strongly with manure N input (r
2 = 0.54 and 0.53, respectively). Seasonal N export varied by basin and was correlated with climate, anthropogenic N inputs,
and reservoir releases. Fractional export of watershed N inputs by study rivers annually was small (median of 8%) and scaled
exponentially with runoff (r = 0.66). Collectively, our results show that anthropogenic activities have altered both the magnitude and timing of watershed
N export in California and suggest that targeted management in specific locations and times of the year could reduce N export
to downstream systems in the region. 相似文献
992.
Thomas Proft 《Biotechnology letters》2010,32(1):1-10
Sortases are transpeptidases produced by Gram-positive bacteria to anchor cell surface proteins covalently to the cell wall.
The Staphylococcus aureus sortase A (SrtA) cleaves a short C-terminal recognition motif (LPXTG) on the target protein followed by the formation of an amide bond with the pentaglycine
cross-bridge in the cell wall. Over recent years, several researchers have exploited this specific reaction for a range of
biotechnology applications, including the incorporation of non-native peptides and non-peptidic molecules into proteins, the
generation of nucleic acid–peptide conjugates and neoglycoconjugates, protein circularisation, and labelling of cell surface
proteins on living cells. 相似文献
993.
The isolation of photosystem-I (PS-I) from spinach has been conducted using ultrafiltration with 300 kDa molecular weight
cut-off polyethersulfone membranes. The effects of ultrafiltration operating conditions on PS-I activity were optimized using
parameter scanning ultrafiltration. These conditions included solution pH, ionic strength, stirring speed, and permeate flux.
The effects of detergent (Triton X-100 and n-dodecyl-beta-D-maltoside) concentration on time dependent activity of PS-I were also studied using an O2 electrode. Under optimized conditions, the PS-I purity obtained in the retentate was about 84% and the activity recovery
was greater than 94% after ultrafiltration. To our knowledge, this is the first report of the isolation of a membrane protein
using ultrafiltration alone. 相似文献
994.
‘Green tides’ are overwhelming the coastline of our blue planet: taking the world’s largest example 总被引:8,自引:0,他引:8
Nai-hao Ye Xiao-wen Zhang Yu-ze Mao Cheng-wei Liang Dong Xu Jian Zou Zhi-meng Zhuang Qing-yin Wang 《Ecological Research》2011,26(3):477-485
A broad spectrum of events that come under the category of green tide are recognized world-wide as a response to elevated
levels of seawater nutrients in coastal areas. Green tides involve a wide diversity of sites, macroalgal species, consequences,
and possible causes. Here we review the effect of natural and man-induced environmental fluctuations on the frequency and
apparent spread of green tides. This article highlights the need for interdisciplinary research aimed at shedding light on
the basic mechanisms governing the occurrence and succession of green algae in coastal seas. This will result in more effective
management and mitigation of the effects of green tides, thus safeguarding the intrinsic and commercial value of coastal marine
ecosystems. 相似文献
995.
Seedlings of two barley genotypes (‘Maresi’ and wild form of Hordeum spontaneum) were treated with jasmonic acid (JA 5 μM and 15 μM) for 24 h, and then subjected to water stress (PEG 6000 solution of −
1.5 MPa). JA caused an increase in the content of ABA but not in that of proline and spermidine in the two studied genotypes.
The effect of the treatment did not depend on the applied JA concentration. The pre-stress treatment with JA changed plant
response to water deficit with regard to membrane injury. Treatment with a lower JA concentration (5 μM) caused a substantial
reduction of the stress-induced membrane damage in the both genotypes. A higher JA concentration (15 μM) caused the reduction
of membrane injury only in H. spontaneum and was ineffective in ‘Maresi’. JA had no influence on the leaf water status in water-stressed plants. A possible role of
JA in leaf ABA accumulation and alleviation of cell membrane injury under water deficit is discussed.
The work was partly supported by the Polish Committee For Scientific Research, grant No 5 PO6A 036 18 相似文献
996.
西南桦人工林与山地雨林的群落学特征比较 总被引:7,自引:0,他引:7
人类活动对生态系统的影响是当今生态学的研究热点之一,但对在退化生态系统上进行人工造林对地带性植被群落学特征的影响研究尚较欠缺。本文根据组成群落的植物生态学特征能对其生态环境做出准确的反应这一规则,通过样地调查法分析了林龄为12年的西南桦(Betula alnoides)人工群落的区系组成和基本的群落学特征,并与当地的地带性植被——山地雨林的区系组成和群落学特征进行了比较,从而探讨人工造林对当地天然生态系统的影响。结果发现,与天然群落相比,人类活动(人工种植西南桦林)对生态系统的植物物种的生活型谱、物种叶型谱、区系成分、物种多样性等方面的群落学特征影响不大;即使在这些方面有或多或少的差异,可能也是小环境的异质性造成的。但是人工种植西南桦林对群落的季相外貌、群落的结构、物种组成、物种丰富度以及生物量等方面有较大的影响。进行综合分析后得出结论:虽然人工造林可以缩短植被自然恢复的时间以及具有显著的经济价值,但与地带性植被相比,还是有较大的生态学差异。建议为了当地经济的发展,有必要适当发展一定面积的人工林,但规模应适度。 相似文献
997.
Xiao Mu Ma Xiao Xia Liu Qing Wen Zhang Jian Zhou Zhao Qing Nian Cai Yong An Ma & Dong Mei Chen 《Entomologia Experimentalis et Applicata》2006,121(3):235-241
The cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae), is an important cotton pest in northern China, especially in the seedling stage of cotton. After large scale commercial use of transgenic Bt cotton, cotton aphids became one of the most important cotton pests. A 2‐year study was conducted to evaluate the role of four winter wheat varieties that were resistant or susceptible to wheat aphid, Sitobion avenae Fabricius (Homoptera: Aphididae), in conserving arthropod natural enemies and suppressing cotton aphids in a wheat–cotton relay intercropping system in northern China. The results indicated that wheat–cotton intercropping preserved and augmented natural enemies more than a monoculture of cotton. The density of natural enemies in cotton was significantly different among relay‐intercropping fields with different wheat varieties. The highest density of natural enemies and low cotton aphid populations were found in the treatment of cotton in relay intercropped with the wheat variety Lovrin10, which is susceptible to wheat aphid. The lowest density of predators and parasitoids associated with high cotton aphid populations were found with the wheat variety KOK1679, which is resistant to wheat aphid. The results showed that wheat varieties that are susceptible or moderately resistant to wheat aphid might reduce cotton aphids more effectively than an aphid‐resistant variety in the intercropping system by enhancing predators to suppress cotton aphids during the cotton seedling stage. 相似文献
998.
Katsunori Motosaka Masayuki Koganezawa Satoko Narikawa Akira Furuyama Kenji Shinozaki Kunio Isono Ichiro Shimada 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2007,193(2):279-283
Acute choice behavior in ingesting two different concentrations of sucrose in Drosophila is presumed to include learning and memory. Effects on this behavior were examined for four mutations that block associative
learning (dunce, rutabaga, amnesiac, and radish). Three of these mutations cause cyclic AMP signaling defects and significantly reduced taste discrimination. The exception
was radish, which affects neither. Electrophysiological recordings confirmed that the sensitivity of taste receptors is almost indistinguishable
in all flies, whether wild type or mutant. These results suggest that food choice behavior in Drosophila involves central nervous learning and memory operating via cyclic AMP signaling pathways. 相似文献
999.
Mariëtte van Amstel Claar de Brauw Peter Driessen Pieter Glasbergen 《Biodiversity and Conservation》2007,16(14):4109-4129
This paper seeks to understand why multinationals prefer to launch a label specific to their own product and examines how
reliable these product-specific eco-labels are. A new methodology is applied to assess the extent to which eco-labels live
up to claims about their contribution to conservation and the sustainable use of agricultural biodiversity. Product-specific
eco-labels are considered as industry self-regulation and all three regulatory stages are studied: the planning, implementation
and outcome stage. There are major differences between the product specific eco-labels in the degree in which agrobiodiversity
management is part of the normative labeling schemes. Although there are some problems of reliability, such as transparency
in the implementation stage and the monitoring in the outcome stage, the degree of reliability of product-specific labels
is comparable with eco-labels of international labeling families. The conclusion is that only one of the product-specific
eco-labels examined here is reliable when examined in the light of all three stages. The main reason why multinationals establish
a product-specific eco-label instead of adopting one from an existing labeling family is that they want to profile themselves
as distinct from other companies. The unique character of a product-specific label creates a market opportunity for them. 相似文献
1000.
microRNA, a family of small non-coding RNA, plays significant roles in regulating gene expression, mainly via binding to the 3′-untranslated region of target genes. Although the role of miRNA in regulating neuroinflammation via the innate immune pathway has been studied, its role in the production of inflammatory mediators during microglial activation is poorly understood. In this study, we investigated the effect of miR-27a on lipopolysaccharide (LPS)-induced microglial inflammation. miR-27a expression was found to be rapidly decreased in microglia by real-time polymerase chain reaction (real-time PCR) after LPS stimulation. Over-expression of miR-27a significantly decreased the production of inflammatory cytokines, such as interleukin-6 (IL-6), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and nitric oxide (NO), whereas knockdown of miR-27a increased the expression of these inflammatory factors. We also demonstrated by loss- and gain-of-function studies that miR-27a directly suppressed the expression of toll-like receptor 4 (TLR4) and interleukin-1 receptor-associated kinase 4 (IRAK4)—a pivotal adaptor kinase in the TLR4/MyD88 signaling pathway—by directly binding their 3′-UTRs: knocking down TLR4 or IRAK4 in microglia significantly decreased TLR4 or IRAK4 expression and inhibited the downstream production of inflammatory mediators. Moreover, the inflammatory cytokines IL-6 and IL-1β were regulated by IRAK4, whereas TNF-α and NO were more dependent on TLR4 activation. Thus, miR-27a might regulate the LPS-induced production of inflammatory cytokines in microglia independently of TLR4 and IRAK4. Taken together, our results suggest that miR-27a is associated with microglial activation and the inflammatory response. 相似文献