全文获取类型
收费全文 | 660篇 |
免费 | 67篇 |
专业分类
727篇 |
出版年
2021年 | 8篇 |
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 14篇 |
2016年 | 18篇 |
2015年 | 25篇 |
2014年 | 33篇 |
2013年 | 18篇 |
2012年 | 22篇 |
2011年 | 31篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 32篇 |
2007年 | 35篇 |
2006年 | 36篇 |
2005年 | 28篇 |
2004年 | 23篇 |
2003年 | 26篇 |
2002年 | 17篇 |
2001年 | 22篇 |
2000年 | 22篇 |
1999年 | 27篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 14篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1972年 | 3篇 |
1969年 | 7篇 |
1935年 | 3篇 |
排序方式: 共有727条查询结果,搜索用时 0 毫秒
1.
S. Dubrou J. Konjek E. Macheras B. Welté L. Guidicelli E. Chignon M. Joyeux J. L. Gaillard B. Heym T. Tully G. Sapriel 《Applied and environmental microbiology》2013,79(18):5498-5508
Nonpigmented and late-pigmenting rapidly growing mycobacteria (RGM) have been reported to commonly colonize water production and distribution systems. However, there is little information about the nature and distribution of RGM species within the different parts of such complex networks or about their clustering into specific RGM species communities. We conducted a large-scale survey between 2007 and 2009 in the Parisian urban tap water production and distribution system. We analyzed 1,418 water samples from 36 sites, covering all production units, water storage tanks, and distribution units; RGM isolates were identified by using rpoB gene sequencing. We detected 18 RGM species and putative new species, with most isolates being Mycobacterium chelonae and Mycobacterium llatzerense. Using hierarchical clustering and principal-component analysis, we found that RGM were organized into various communities correlating with water origin (groundwater or surface water) and location within the distribution network. Water treatment plants were more specifically associated with species of the Mycobacterium septicum group. On average, M. chelonae dominated network sites fed by surface water, and M. llatzerense dominated those fed by groundwater. Overall, the M. chelonae prevalence index increased along the distribution network and was associated with a correlative decrease in the prevalence index of M. llatzerense, suggesting competitive or niche exclusion between these two dominant species. Our data describe the great diversity and complexity of RGM species living in the interconnected environments that constitute the water production and distribution system of a large city and highlight the prevalence index of the potentially pathogenic species M. chelonae in the distribution network. 相似文献
2.
The equine leucocyte antigen (ELA) types and the clinical diagnosis for equine sarcoid and summer dermatitis were evaluated in 2026 horses representing five breeds. Data were analysed in unrelated animals and in family material. In the case of equine sarcoid, a strong association was observed between the ELA class II DW13 antigen and its effect on Swiss (cP < 0·001), French (cP < 0·0001) and Irish (cP < 0·01) Warmblood horses. The class I antigen A3 occurred more frequently in sarcoid-affected French horses (cP < 0·001). These results confirm our earlier findings (Gerber et al. 1988). Among Freiberger horses, which lack the ELA DW13 and A3 specificities, a breed-specific class I antigen, ABe108, displayed an increased frequency (cP < 0·05) in the affected group. Among Arabian horses, a tendency for increased frequency of the A1 antigen was observed in the affected animals, but the number of affected horses is too small for statistical significance. The Mendelian segregation in diseased half-siblings by ELA DW13 heterozygous stallions showed a strong association (P < 0·0001) between the inherited DW13 antigen and susceptibility to the sarcoid effect. In the case of summer dermatitis, previously published data (Marti et al. 1992) have been extended. The ELA types in four multiple-case families, founded by the same stallion, were analysed for an association with the effect of sarcoid. Eight out of nine ELA-typed affected offspring inherited the paternal haplotype A15, DW23 in contrast to nonaffected offspring where three out of 12 displayed these antigens (P < 0·005). Moreover, the ELA haplotypes of 11 out of 12 informative affected half-siblings sired by another stallion inherited the paternal haplotype A3, W12, DW23 (P < 0·05). Our findings demonstrate statistically significant associations between certain ELA antigens and two equine diseases. It is still unknown if the major histocompatibility complex (MHC) molecules themselves or another linked gene(s) play a role in the pathogenesis of these conditions. 相似文献
3.
C Chatelet J Gaillard Y Pétillot M Louwagie J Meyer 《Biochemical and biophysical research communications》1999,261(3):885-889
Overexpression in Escherichia coli of the fdx4 gene from Aquifex aeolicus has allowed isolation and characterization of the first hyperthermophilic [2Fe-2S](Scys)(4) protein, a homodimer of M = 2 x 12.4 kDa with one [2Fe-2S] cluster per subunit. This protein is undamaged by heating to 100 degrees C for at least three hours. The primary structure, in particular the characteristic distribution of the four cysteine ligands of the metal site, and the spectroscopic properties of the A. aeolicus protein relate it to well characterized [2Fe-2S] proteins from Clostridium pasteurianum and Azotobacter vinelandii. These proteins are also homologous to subunits or domains of hydrogenases and NADH-ubiquinone oxidoreductase (Complex I) of respiratory chains. The A. aeolicus [2Fe-2S] protein is thus representative of a presumably novel protein fold involved in a variety of functions in very diverse cellular backgrounds. 相似文献
4.
5.
G Guillon R C Gaillard P Kehrer P Schoenenberg A F Muller S Jard 《Regulatory peptides》1987,18(3-4):119-129
Adenohypophysial cells from female Wistar rats were dispersed and maintained for 4 days in primary culture in the presence of [3H]myoinositol. The effects of several releasing hormones, corticotropin-releasing factor (CRF), arginine vasopressin (AVP), angiotensin II (A II), thyrotropin-releasing hormone (TRH), and luteinizing hormone-releasing hormone (LHRH) on the liberation of labelled inositol phosphate (InsP), inositol-bisphosphate (InsP2), and inositol-trisphosphate (InsP3) from prelabelled inositol lipids were tested alone and in combination. Of the corticotropin (ACTH) secretagogues tested, AVP and A II produced a dose-dependent increase in inositol phosphate accumulation. CRF was inactive. The ED50 values of about 1 nM for both AVP and A II were close to the corresponding dissociation constants for binding to pituitary membranes: and, in the case of A II, close to the ED50 for A II-induced inhibition of pituitary membrane adenylate cyclase. The responses to A II and AVP could be inhibited by [Sar1,Ile8]A II and the AVP antagonist d(Et2)-VAVP, respectively. The magnitude of the maximal effect of AVP on accumulation of inositol phosphates was small (25% increase over basal value) suggesting that this effect was restricted to a minor subpopulation of pituitary cells (probably corticotrophes). CRF did not potentiate AVP-induced inositol phosphates accumulation. Maximal A II-induced increase in inositol phosphates accumulation represented 150% of the basal value and was partially additive with that of TRH suggesting that lactotrophes represent the main A II-sensitive subpopulation. 相似文献
6.
R. Garcia F. Gaillard J. -C. Jacquenod 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1988,162(4):443-451
Ipsilateral retino-tecto-tectal (IRTT) units were recorded extracellularly in the rostral optic tectum of the frog (Rana esculenta). The activity of 79 superficial units (II type) was quantified in response to black disks of various sizes, moved vertically at various angular velocities and against a white background. The contrast ¦C¦ was constant during the experiments. Neuronal activity was analysed by two methods, yielding identical results:
The results show that qualitatively and quantitatively, the properties of I1 units are very similar to R1–R2 (sustained) ganglion cells. 相似文献
(1) | I1 units responded transiently to moving and movement gated stationary stimuli; these units did not seem to be directionally sensitive nor responsive to changes in background illumination. Fifty-three % of units had a low spontaneous activity. |
(2) | A power function relating mean firing frequency (¯R) and angular velocity (v) was established in the majority (78%) of units. The exponent and the constantk were 0.44–0.8 and 8.9–20, respectively. |
(3) | The relationship between¯R and stimulus diameter (D) was best expressed by a logarithmic function. The maximum response occurred forD= 2–4. The optimal stimulus diameter was found to be independent of stimulus velocity. |
(4) | When stimulated repetitively under steady conditions, I1 units showed about 10% fluctuations in mean response, which seemed to increase with stimulus diameter. |
7.
Hydrogen-1 nuclear magnetic resonance of the nitrogenase iron protein (Cp2) from Clostridium pasteurianum 总被引:1,自引:0,他引:1
Proton NMR spectra (250 MHz) of the nitrogenase iron protein from Clostridium pasteurianum (Cp2) were found to display 9 or 10 paramagnetically shifted resonances in the 15-50 ppm range. The most shifted resonances belonged to two approximately equal subsets having temperature dependences of opposite sign. The latter occurrence is consistent with the interaction of the corresponding protons with an antiferromagnetically coupled metal center. The number of proton resonances of Cp2, their positions, and their temperature dependences were similar to those observed in spectra of (4Fe-4S)+ ferredoxins, particularly those of the latter that contain a single tetranuclear cluster, such as the ferredoxin from Bacillus stearothermophilus. The effects of several adenine nucleotides on the paramagnetically shifted proton resonances of Cp2 have been investigated. Whereas MgAMP had no effect at all, MgADP and MgATP were found to induce different modifications, which in both cases involved approximately half only of the shifted proton resonances. These data suggest that nucleotide binding affects mainly one part of the iron-sulfur cluster. A remarkable feature of the spectra of Cp2 in the presence of MgATP is the grouping of the shifted proton resonances in sets of two or four having identical chemical shifts and temperature dependences. A nearly perfect 2-fold symmetry is thus suggested for the arrangement of the cysteine protons around the active site. These observations lend support to the proposal that the (4Fe-4S) cluster is held symmetrically between the two identical subunits and are consistent with the existence of two MgATP binding sites on nitrogenase iron proteins.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
8.
Morphological and metabolic characterization of a new species of strictly anaerobic rumen fungus: Neocallimastix joyonii 总被引:2,自引:0,他引:2
André Breton Annick Bernalier Frédérique Bonnemoy Gérard Fonty Brigitte Gaillard Philippe Gouet 《FEMS microbiology letters》1989,58(2-3):309-314
A new strain of strictly anaerobic fungi was isolated from the rumen of sheep. This strain is characterized by a polycentric thallus, an extensive and polynuclear rhizomycelium, polyflagellated zoospores with gamma particle-like bodies. We propose to assign this strain in a new species: Neocallimastix joyonii. 相似文献
9.
I al-Timimi J L Gaillard H Amri P Silberzahn 《The Journal of biological chemistry》1989,264(13):7161-7168
Whereas mare corpus luteum does not produce androgens or estrogens in vivo, the incubation of mare corpus luteum microsomes with progesterone and NADPH resulted in 17 alpha-hydroxyprogesterone and estrogen production with a small yield of androstenedione. In the presence of an aromatase inhibitor (4-hydroxyandrostenedione), 17 alpha-hydroxyprogesterone and androstenedione were accumulated. Aromatization of testosterone and androstenedione occurred via stereospecific loss of the 1 beta, 2 beta hydrogen atoms and was inhibited by MgCl2, KCl, and EDTA. The Km of estrogen synthetase from equine corpus luteum for testosterone was 18.5 +/- 2.7 nM and for androstenedione was 11.5 +/- 1.5 nM. 19-Norandrogens were aromatized with a slightly higher efficiency than were androgens, but the affinity of the aromatase was lower for 19-norandrogens than for androgens. Our results suggest that aromatases from equine testis and corpus luteum are closely related enzymes. On the other hand, the question arises as to the relationship among the cell origin, the synthetizing abilities, and in vivo production of the corpus luteum in different mammalian species. 相似文献
10.
The 1H resonances of the high-potential [4Fe-4S]2+ ferredoxin from Chromatium vinosum have been assigned through conventional sequential methodology applied to 2D NMR spectra. Almost 80% of the residues were identified using standard 2D COSY, HOHAHA, and NOESY pulse sequences. These residues correspond to four segments of the primary structure that do not interact strongly with the iron-sulfur cluster. A minor correction to the amino acid sequence is strongly suggested by these NMR data. Additional protons more sensitive to the proximity of the cluster were assigned by a combination of NOESY experiments with fast repetition rates and short mixing times and of HOHAHA spectra recorded with reduced spin-lock duration aimed at compensating for the short relaxation rates. Hence, the contributions of 79 residues out of 85 were identified in NMR spectra, among which the assignments of 64 residues were completed. Even the fastest relaxing protons, like those of the cysteine ligands, could be correlated, partly because the strong hyperfine shifts isolate them from the crowded diamagnetic region. However, other protons, in particular those involved in NH-S hydrogen bonds with the iron-sulfur cluster, were more difficult to identify, most probably because their relatively broad signals overlapped with those of protons not or less perturbed by the active site. The availability of the major part of the 1H NMR assignments has enabled the detection and identification of many interresidue NOESY cross peaks. These data are in full agreement with the elements of secondary structure previously revealed by X-ray crystallographic analysis of the protein.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献