全文获取类型
收费全文 | 11512篇 |
免费 | 1127篇 |
国内免费 | 5篇 |
出版年
2023年 | 94篇 |
2022年 | 212篇 |
2021年 | 385篇 |
2020年 | 216篇 |
2019年 | 281篇 |
2018年 | 307篇 |
2017年 | 256篇 |
2016年 | 429篇 |
2015年 | 745篇 |
2014年 | 770篇 |
2013年 | 781篇 |
2012年 | 1103篇 |
2011年 | 1014篇 |
2010年 | 549篇 |
2009年 | 424篇 |
2008年 | 590篇 |
2007年 | 634篇 |
2006年 | 503篇 |
2005年 | 447篇 |
2004年 | 466篇 |
2003年 | 348篇 |
2002年 | 335篇 |
2001年 | 81篇 |
2000年 | 87篇 |
1999年 | 83篇 |
1998年 | 87篇 |
1997年 | 49篇 |
1996年 | 51篇 |
1995年 | 35篇 |
1994年 | 52篇 |
1993年 | 59篇 |
1992年 | 70篇 |
1991年 | 70篇 |
1990年 | 63篇 |
1989年 | 48篇 |
1988年 | 42篇 |
1987年 | 45篇 |
1986年 | 35篇 |
1985年 | 53篇 |
1984年 | 50篇 |
1983年 | 37篇 |
1982年 | 40篇 |
1981年 | 38篇 |
1980年 | 37篇 |
1979年 | 38篇 |
1978年 | 39篇 |
1976年 | 41篇 |
1975年 | 28篇 |
1974年 | 41篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Rieping W Habeck M Bardiaux B Bernard A Malliavin TE Nilges M 《Bioinformatics (Oxford, England)》2007,23(3):381-382
Modern structural genomics projects demand for integrated methods for the interpretation and storage of nuclear magnetic resonance (NMR) data. Here we present version 2.1 of our program ARIA (Ambiguous Restraints for Iterative Assignment) for automated assignment of nuclear Overhauser enhancement (NOE) data and NMR structure calculation. We report on recent developments, most notably a graphical user interface, and the incorporation of the object-oriented data model of the Collaborative Computing Project for NMR (CCPN). The CCPN data model defines a storage model for NMR data, which greatly facilitates the transfer of data between different NMR software packages. Availability: A distribution with the source code of ARIA 2.1 is freely available at http://www.pasteur.fr/recherche/unites/Binfs/aria2. 相似文献
932.
Sommer MS Gould SB Lehmann P Gruber A Przyborski JM Maier UG 《Molecular biology and evolution》2007,24(4):918-928
Phototrophic chromalveolates possess plastids surrounded by either 3 or 4 membranes, revealing their secondary endosymbiotic origin from an engulfed eukaryotic alga. In cryptophytes, a member of the chromalveolates, the organelle is embedded within a designated region of the host's rough endoplasmic reticulum (RER). Its eukaryotic compartments other than the plastid were reduced to the mere remains of its former cytosol, the periplastid compartment (PPC, PP space), and its nucleus, the nucleomorph, separated from the RER by its former plasma membrane, the periplast membrane (PPM). In the nucleomorph genome of the cryptophyte Guillardia theta, we identified several genes sharing homology with components of the ER-associated degradation (ERAD) machinery of yeast and higher eukaryotes, namely ORF201 and ORF477, homologs of membrane-bound proteins, Der1p (Degradation in the ER protein 1) and the RING-finger ubiquitin ligase Hrd1, and a truncated version of Udf1, a cofactor of Cdc48, a lumenal ATPase. Exemplarily, studies on the Der1-homolog ORF201 showed that this protein partially rescued a yeast deletion mutant, indicating the existence of a functional PPC-specific ERAD-like system in cryptophytes. With the noninvestigated exception of haptophytes a phylogenetically and mechanistically related system is apparently present in all chromalveolates with 4 membrane-bound plastids because amongst others, PPC-specific Derlins (Der1-like proteins), CDC48 and its cofactor Ufd1 were identified in the nuclear genomes of diatoms and apicomplexa. These proteins are equipped with the required topogenic signals to direct them into the periplastid compartment of their secondary symbionts. Based on our findings, we suggest that all chromalveolates with 4 membrane-bound plastids express an ERAD-derived machinery in the PPM of their secondary plastid, coexisting physically and systematically adjacent to the host's own ERAD system. We propose herewith that this system was functionally adapted to mediate transport of nucleus-encoded PPC/plastid preproteins from the RER into the periplastid space. 相似文献
933.
Escherichia coli K (JM109) and E. coli B (BL21) are strains used routinely for recombinant protein production. These two strains grow and respond differently to environmental factors such as glucose and oxygen concentration. The differences have been attributed to differential expression of individual genes that constitute certain metabolic pathways that are part of the central carbon metabolism. By implementing a semiparametric algorithm, which is based on a density ratio model, it was possible to compare and quantify the expression patterns of groups of genes involved in several central carbon metabolic pathways. The groups comprising the glyoxylate shunt, TCA cycle, fatty acid, and gluconeogenesis and anaplerotic pathways were expressed differently between the two strains, whereas no differences were apparent for the groups comprising either glycolysis or the pentose phosphate pathway. These results further characterized differences between the two E. coli strains and illustrated the potency of the semiparametric algorithm. 相似文献
934.
Correction of fragile X syndrome in mice 总被引:5,自引:0,他引:5
935.
Chemical shift assignment is the first step in all established protocols for structure determination of uniformly labeled
proteins by NMR. The explosive growth in recent years of magic-angle spinning (MAS) solid-state NMR (SSNMR) applications is
largely attributable to improved methods for backbone and side-chain chemical shift correlation spectroscopy. However, the
techniques developed so far have been applied primarily to proteins in the size range of 5–10 kDa, despite the fact that SSNMR
has no inherent molecular weight limits. Rather, the degeneracy inherent to many 2D and 3D SSNMR spectra of larger proteins
has prevented complete unambiguous chemical shift assignment. Here we demonstrate the implementation of 4D backbone chemical
shift correlation experiments for assignment of solid proteins. The experiments greatly reduce spectral degeneracy at a modest
cost in sensitivity, which is accurately described by theory. We consider several possible implementations and investigate
the CANCOCX pulse sequence in detail. This experiment involves three cross polarization steps, from H to CA[i], CA[i] to N[i],
and N[i] to C′[i−1], followed by a final homonuclear mixing period. With short homonuclear mixing times (<20 ms), backbone
correlations are observed with high sensitivity; with longer mixing times (>200 ms), long-range correlations are revealed.
For example, a single 4D experiment with 225 ms homonuclear mixing time reveals ∼200 uniquely resolved medium and long-range
correlations in the 56-residue protein GB1. In addition to experimental demonstrations in the 56-residue protein GB1, we present
a theoretical analysis of anticipated improvements in resolution for much larger proteins and compare these results in detail
with the experiments, finding good agreement between experiment and theory under conditions of stable instrumental performance. 相似文献
936.
Cytotoxin fractions were isolated from Campylobacter jejuni 81116 and semi-purified by size-exclusion liquid chromatography. The fraction showing the strongest toxicity was injected into mice to produce antiserum. The antiserum was used to screen a C. jejuni 81116 cosmid library. Nine genes were identified in overlapping cosmid inserts that induced reactivity with the antiserum. One of these genes showed high similarity to a periplasmic protein of unknown function and its isogenic mutant showed decreased toxicity compared to the C. jejuni 81116 wild type. This gene contains a Gram-negative bacterial RTX toxin-activating protein C signature, which suggests it may play a role in C. jejuni 81116 cytotoxin activation. 相似文献
937.
938.
Background
Phylogenies of rapidly evolving pathogens can be difficult to resolve because of the small number of substitutions that accumulate in the short times since divergence. To improve resolution of such phylogenies we propose using insertion and deletion (indel) information in addition to substitution information. We accomplish this through joint estimation of alignment and phylogeny in a Bayesian framework, drawing inference using Markov chain Monte Carlo. Joint estimation of alignment and phylogeny sidesteps biases that stem from conditioning on a single alignment by taking into account the ensemble of near-optimal alignments. 相似文献939.
Disturbance persistence in managed grasslands: shifts in aboveground community structure and the weed seed bank 总被引:2,自引:0,他引:2
The length of time and form in which disturbances persist in systems depends on the intensity and frequency of disturbance
and on the abilities of resident species to recover from such events. In grazed grasslands, trampling by large mammalian herbivores
can periodically facilitate weed establishment by exposing patches of bare ground but whether an intense soil disturbance
event results in a temporary increase in weed abundance or a persistent weed problem remains unclear. In May 2002, cattle
trampling following heavy rain caused severe damage to nine-month old, rotationally grazed, cool-season pastures (Midwest
USA). In September 2002, we compared the aboveground composition of paddocks (i.e., fenced pasture sections) that were heavily
disturbed to those that received no damage. Relative to undisturbed paddocks, forage species relative cover was 17% lower
in disturbed paddocks, and weed species and bare ground relative cover was 61% and 100% higher, respectively. By September
2004, paddock types did not differ in all aboveground community components. However, the abundance and species richness of
weed seeds in the soil seed bank averaged respectively 82% and 30% higher in disturbed paddocks between 2003 and 2004. These
findings indicate that a spatially extensive, intense soil disturbance event may soon become undetectable in components of
aboveground pasture structure but can persist as an augmented weed seed bank. Because of high weed seed bank longevity, disturbances
to formerly disturbed pastures would likely result in higher weed recruitment, with more species represented, than in those
which lack previous disturbance. Disturbance history may thus be a useful predictor of weed community composition following
subsequent disturbance. Based on empirical data supporting this proposition, we recommend that grassland managers explicitly
incorporate disturbance history into dynamic management planning and do not rely exclusively on aboveground characters to
evaluate the invasion status or colonization potential of an area by undesirable plants. We emphasize that the ecological
legacies of past soil disturbance events cannot only influence the contemporary patterns and processes of grasslands, but
importantly, affect their compositional trajectories following subsequent perturbation. 相似文献
940.