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991.
Myron J. Mitchell Gary Lovett Scott Bailey Fred Beall Doug Burns Don Buso Thomas A. Clair Francois Courchesne Louis Duchesne Cathy Eimers Ivan Fernandez Daniel Houle Dean S. Jeffries Gene E. Likens Michael D. Moran Christopher Rogers Donna Schwede Jamie Shanley Kathleen C. Weathers Robert Vet 《Biogeochemistry》2011,103(1-3):181-207
Most of eastern North America receives elevated levels of atmospheric deposition of sulfur (S) that result from anthropogenic SO2 emissions from fossil fuel combustion. Atmospheric S deposition has acidified sensitive terrestrial and aquatic ecosystems in this region; however, deposition has been declining since the 1970s, resulting in some recovery in previously acidified aquatic ecosystems. Accurate watershed S mass balances help to evaluate the extent to which atmospheric S deposition is retained within ecosystems, and whether internal cycling sources and biogeochemical processes may be affecting the rate of recovery from decreasing S atmospheric loads. This study evaluated S mass balances for 15 sites with watersheds in southeastern Canada and northeastern US for the period 1985 to 2002. These 15 sites included nine in Canada (Turkey Lakes, ON; Harp Lake, ON; Plastic Lake, ON; Hermine, QC; Lake Laflamme, QC; Lake Clair, QC; Lake Tirasse, QC; Mersey, NS; Moosepit, NS) and six in the US (Arbutus Lake, NY; Biscuit Brook, NY; Sleepers River, VT; Hubbard Brook Experimental Forest, NH; Cone Pond, NH; Bear Brook Watershed, ME). Annual S wet deposition inputs were derived from measured bulk or wet-only deposition and stream export was obtained by combining drainage water fluxes with SO4 2? concentrations. Dry deposition has the greatest uncertainty of any of the mass flux calculations necessary to develop accurate watershed balances, and here we developed a new method to calculate this quantity. We utilized historical information from both the US National Emissions Inventory and the US (CASTNET) and the Canadian (CAPMoN) dry deposition networks to develop a formulation that predicted SO2 concentrations as a function of SO2 emissions, latitude and longitude. The SO2 concentrations were used to predict dry deposition using relationships between concentrations and deposition flux derived from the CASTNET or CAPMoN networks. For the year 2002, we compared the SO2 concentrations and deposition predictions with the predictions of two continental-scale air quality models, the Community Multiscale Air Quality (CMAQ) model and A Unified Regional Air-quality Modeling System (AURAMS) that utilize complete inventories of emissions and chemical budgets. The results of this comparison indicated that the predictive relationship provides an accurate representation of SO2 concentrations and S deposition for the region that is generally consistent with these models, and thus provides confidence that our approach could be used to develop accurate watershed S budgets for these 15 sites. Most watersheds showed large net losses of SO4 2? on an annual basis, and the watershed mass balances were grouped into five categories based on the relative value of mean annual net losses or net gains. The net annual fluxes of SO4 2? showed a strong relationship with hydrology; the largest net annual negative fluxes were associated with years of greatest precipitation amount and highest discharge. The important role of catchment hydrology on S budgets suggests implications for future predicted climate change as it affects patterns of precipitation and drought. The sensitivity of S budgets is likely to be greatest in watersheds with the greatest wetland area, which are particularly sensitive to drying and wetting cycles. A small number of the watersheds in this analysis were shown to have substantial S sources from mineral weathering, but most showed evidence of an internal source of SO4 2?, which is likely from the mineralization of organic S stored from decades of increased S deposition. Mobilization of this internal S appears to contribute about 1?C6 kg S ha?1 year?1 to stream fluxes at these sites and is affecting the rate and extent of recovery from acidification as S deposition rates have declined in recent years. This internal S source should be considered when developing critical deposition loads that will promote ecosystem recovery from acidification and the depletion of nutrient cations in the northeastern US and southeastern Canada. 相似文献
992.
Nucleotide binding domains (NBD1 and NBD2) of the cystic fibrosis transmembrane conductance (CFTR), the defective protein
in cystic fibrosis, are responsible for controlling the gating of the chloride channel and are the putative binding site for
several candidate drugs in the disease treatment. We studied the structural properties of recombinant NBD1, NBD2, and an equimolar
NBD1/NBD2 mixture in solution by small-angle X-ray scattering. We demonstrated that NBD1 or NBD2 alone have an overall structure
similar to that observed for crystals. Application of 2 mM ATP induces a dimerization of NBD1 but does not modify the NBD2
monomeric conformation. An equimolar mixture of NBD1/NBD2 in solution shows a dimeric conformation, and the application of
ATP to the solution causes a conformational change in the NBD1/NBD2 complex into a tight heterodimer. We hypothesize that
a similar conformation change occurs in situ and that transition is part of the gating mechanism. To our knowledge, this is
the first direct observation of a conformational change of the NBD1/NBD2 interaction by ATP. This information may be useful
to understand the physiopathology of cystic fibrosis. 相似文献
993.
994.
Moran TB Goldberg LB Serviss SL Raetzman LT 《Molecular endocrinology (Baltimore, Md.)》2011,25(1):117-127
The pituitary gland contains six distinct hormone-secreting cell types that are essential for basic physiological processes including fertility and responding to stress. Formation of hormone-secreting cells during development relies on Notch signaling to prevent progenitors from prematurely differentiating. The nature of the signal curtailing Notch signaling in the pituitary is unknown, but a good candidate is the endocytic adaptor protein NUMB. NUMB targets Notch for proteolytic degradation, but it also has a broad range of actions, including stabilizing adherens junctions through interactions with cadherins and influencing cell proliferation by stabilizing expression of the tumor suppressor protein p53. Here, we show that NUMB and its closely related homolog, NUMBLIKE, are expressed in undifferentiated cells during development and later in gonadotropes in the anterior lobe and melanotropes of the intermediate lobe. All four isoforms of NUMB, are detectable in the pituitary, with the shorter forms becoming more prominent after adolescence. Conditionally deleting Numb and Numblike in the intermediate lobe melanotropes with Pomc Cre mice dramatically alters the morphology of cells in the intermediate lobe, coincident with impaired localization of adherens junctions proteins including E-CADHERIN, N-CADHERIN, β-CATENIN, and α-CATENIN. Strikingly, the border between posterior and intermediate lobes is also disrupted. These mice also have disorganized progenitor cells, marked by SOX2, but proliferation is unaffected. Unexpectedly, Notch activity appears normal in conditional knockout mice. Thus, Numb is critical for maintaining cell-cell interactions in the pituitary intermediate lobe that are essential for proper cell placement. 相似文献
995.
Apoptosis-inducing factor (AIF) is implicated in caspase-independent apoptotic-like death. AIF released from mitochondria translocates to the nucleus, where it mediates some apoptotic events such as chromatin condensation and DNA degradation. Here, the role of AIF in the neuronal death was studied under physiological conditions. When we analyzed the cellular localization of AIF during cerebellar development, we found a significant increase in the number of neurons with nuclear AIF localization in an age-dependent manner. On the other hand, cerebellar granule neurons (CGN) chronically cultured in low concentration of potassium (5 mM; K5) die with apoptotic-like characteristics after five days. In the present study we found that K5 induces a caspase-dependent apoptotic-like death of CGN as well as a late nuclear translocation of AIF. When CGN death induced by K5 was carried out in the presence of a general inhibitor of caspases, there was a slight decrement of cell death, but neurons eventually died by showing apoptotic-like features such as phosphatidylserine translocation and nuclear condensation. Besides, there was a significant increment of nuclear AIF translocation. These findings support the idea that AIF could be involved in apoptotic-like death of CGN and that it could be an alternative mechanism of neuronal death during cerebellar development. 相似文献
996.
Degnan PH Bittleston LS Hansen AK Sabree ZL Moran NA Almeida RP 《Current microbiology》2011,62(5):1565-1572
Eukaryotes engage in intimate interactions with microbes that range in age and type of association. Although many conspicuous
examples of ancient insect associates are studied (e.g., Buchnera
aphidicola), fewer examples of younger associations are known. Here, we further characterize a recently evolved bacterial endosymbiont
of the leafhopper Euscelidius variegatus (Hemiptera, Cicadellidae), called BEV. We found that BEV, continuously maintained in E. variegatus hosts at UC Berkeley since 1984, is vertically transmitted with high fidelity. Unlike many vertically transmitted, ancient
endosymbioses, the BEV–E. variegatus association is not obligate for either partner, and BEV can be cultivated axenically. Sufficient BEV colonies were grown
and harvested to estimate its genome size and provide a partial survey of the genome sequence. The BEV chromosome is about
3.8 Mbp, and there is evidence for an extrachromosomal element roughly 53 kb in size (e.g., prophage or plasmid). We sequenced
438 kb of unique short-insert clones, representing about 12% of the BEV genome. Nearly half of the gene fragments were similar
to mobile DNA, including 15 distinct types of insertion sequences (IS). Analyses revealed that BEV not only shares virulence
genes with plant pathogens, but also is closely related to the plant pathogenic genera Dickeya, Pectobacterium, and Brenneria. However, the slightly reduced genome size, abundance of mobile DNA, fastidious growth in culture, and efficient vertical
transmission suggest that symbiosis with E. variegatus has had a significant impact on genome evolution in BEV. 相似文献
997.
998.
A network of dynamic protein interactions with their protein partners, substrates, and ligands is known to be crucial for biological function. Revealing molecular and structural-based mechanisms at atomic resolution and in real-time is fundamental for achieving a basic understanding of cellular processes. These technically challenging goals may be achieved by combining time-resolved spectroscopic and structural-kinetic tools, thus providing broad insights into specific molecular events over a wide range of timescales. Here we review representative studies utilizing such an integrated real-time structural approach designed to reveal molecular mechanisms underlying protein interactions at atomic resolution. 相似文献
999.
1000.
Xueping Li Yada Treesukosol Alexander Moghadam Megan Smith Erica Ofeldt Dejun Yang Tianxia Li Kellie Tamashiro Pique Choi Timothy H. Moran Wanli W. Smith 《PloS one》2014,9(5)
Synphilin-1 is a cytoplasmic protein that has been shown to be involved in the control of energy balance. Previously, we reported on the generation of a human synphilin-1 transgenic mouse model (SP1), in which overexpression of human synphilin-1 resulted in hyperphagia and obesity. Here, behavioral measures in SP1 mice were compared with those of their age-matched controls (NTg) at two time points: when there was not yet a group body weight difference (“pre-obese”) and when SP1 mice were heavier (“obese”). At both time points, meal pattern analyses revealed that SP1 mice displayed higher daily chow intake than non-transgenic control mice. Furthermore, there was an increase in meal size in SP1 mice compared with NTg control mice at the obese stage. In contrast, there was no meal number change between SP1 and NTg control mice. In a brief-access taste procedure, both “pre-obese” and “obese“ SP1 mice displayed concentration-dependent licking across a sucrose concentration range similar to their NTg controls. However, at the pre-obese stage, SP1 mice initiated significantly more trials to sucrose across the testing sessions and licked more vigorously at the highest concentration presented, than the NTg counterparts. These group differences in responsiveness to sucrose were no longer apparent in obese SP1 mice. These results suggest that at the pre-obese stage, the increased trials to sucrose in the SP1 mice reflects increased appetitive behavior to sucrose that may be indicative of the behavioral changes that may contribute to hyperphagia and development of obesity in SP1 mice. These studies provide new insight into synphilin-1 contributions to energy homeostasis. 相似文献