全文获取类型
收费全文 | 10900篇 |
免费 | 997篇 |
国内免费 | 8篇 |
出版年
2021年 | 91篇 |
2019年 | 82篇 |
2018年 | 112篇 |
2017年 | 125篇 |
2016年 | 179篇 |
2015年 | 333篇 |
2014年 | 311篇 |
2013年 | 435篇 |
2012年 | 572篇 |
2011年 | 529篇 |
2010年 | 379篇 |
2009年 | 307篇 |
2008年 | 491篇 |
2007年 | 510篇 |
2006年 | 458篇 |
2005年 | 542篇 |
2004年 | 468篇 |
2003年 | 450篇 |
2002年 | 438篇 |
2001年 | 173篇 |
2000年 | 150篇 |
1999年 | 162篇 |
1998年 | 150篇 |
1997年 | 115篇 |
1996年 | 117篇 |
1995年 | 112篇 |
1994年 | 94篇 |
1993年 | 129篇 |
1992年 | 128篇 |
1991年 | 138篇 |
1990年 | 132篇 |
1989年 | 139篇 |
1988年 | 140篇 |
1987年 | 111篇 |
1986年 | 117篇 |
1985年 | 90篇 |
1984年 | 96篇 |
1983年 | 88篇 |
1982年 | 91篇 |
1981年 | 123篇 |
1980年 | 95篇 |
1979年 | 117篇 |
1978年 | 106篇 |
1977年 | 99篇 |
1975年 | 83篇 |
1974年 | 110篇 |
1973年 | 113篇 |
1972年 | 87篇 |
1970年 | 96篇 |
1969年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
231.
232.
Sulfonates: novel electron acceptors in anaerobic respiration 总被引:8,自引:0,他引:8
Thomas J. Lie Thomas Pitta E. R. Leadbetter Walter Godchaux III. Jared R. Leadbetter 《Archives of microbiology》1996,166(3):204-210
The enrichment and isolation in pure culture of a bacterium, identified as a strain of Desulfovibrio, able to release and reduce the sulfur of isethionate (2-hydroxyethanesulfonate) and other sulfonates to support anaerobic
respiratory growth, is described. The sulfonate moiety was the source of sulfur that served as the terminal electron acceptor,
while the carbon skeleton of isethionate functioned as an accessory electron donor for the reduction of sulfite. Cysteate
(alanine-3-sulfonate) and sulfoacetaldehyde (acetaldehyde-2-sulfonate) could also be used for anaerobic respiration, but many
other sulfonates could not. A survey of known sulfate-reducing bacteria revealed that some, but not all, strains tested could
utilize the sulfur of some sulfonates as terminal electron acceptor. Isethionate-grown cells of Desulfovibrio strain IC1 reduced sulfonate-sulfur in preference to that of sulfate; however, sulfate-grown cells reduced sulfate-sulfur
in preference to that of sulfonate.
Received: 2 May 1996 / Accepted: 8 June 1996 相似文献
233.
Jane Stratford Michael A. Wright Walter Reineke Heiner Mokross Jurgen Havel Christopher J. Knowles Gary K. Robinson 《Archives of microbiology》1996,165(3):213-218
Chlorobenzoates (CBA) arise as intermediates during the degradation of polychlorinated biphenyls (PCBs) and some chlorinated herbicides. Since PCBs were produced as complex mixtures, a range of mono-, di-, and possibly trichloro-substituted benzoates would be formed. Chlorobenzoate degradation has been proposed to be one of the rate-limiting steps in the overall PCB-degradation process. Three hybrid bacteria constructed to have the ability to completely mineralise 2-, 3-, or 4-monochlorobiphenyl respectively, have been studied to establish the range of mono- and diCBAs that can be utilised. The three strains were able to mineralise one or more of the following CBAs: 2-, 3-, and 4-monochlorobenzoate and 3,5-dichlorobenzoate. No utilisation of 2,3-, 2,5-, 2,6-, or 3,4-diCBA was observed, and only a low concentration (0.11 mM) of 2,4-diCBA was mineralised. When the strain with the widest substrate range (Burkholderia cepacia JHR22) was simultaneously supplied with two CBAs, one that it could utilise plus one that it was unable to utilise, inhibitory effects were observed. The utilisation of 2-CBA (2.5 mM) by this strain was inhibited by 2,3-CBA (200 M) and 3,4-CBA (50 M). Although 2,5-CBA and 2,6-CBA were not utilised as carbon sources by strain JHR22, they did not inhibit 2-CBA utilisation at the concentrations studied, whereas 2,4-CBA was co-metabolised with 2-CBA. The utilisation of 2-, 3-, and 4-chlorobiphenyl by strain JHR22 was also inhibited by the presence of 2,3- or 3,4-diCBA. We conclude that the effect of the formation of toxic intermediates is an important consideration when designing remediation strategies.Abbreviations
PCB
Polychlorinated biphenyl
-
CBA
Chlorobenzoate 相似文献
234.
Effects of plant size on photosynthesis and water relations in the desert shrub Prosopis glandulosa (Fabaceae) 总被引:1,自引:0,他引:1
Amrita G. de Soyza Augusto C. Franco Ross A. Virginia James F. Reynolds Walter G. Whitford 《American journal of botany》1996,83(1):99-105
The Jornada del Muerto basin of the Chihuahuan Desert of southern New Mexico, USA, has undergone a marked transition of plant communities. Shrubs such as mesquite (Prosopis glandulosa) have greatly increased or now dominate in areas that were previously dominated by perennial grasses. The replacement of grasses by shrubs requires an establishment phase where small shrubs must compete directly with similar-sized grass plants. This is followed by a phase in which large, established shrubs sequester nutrients and water within their biomass and alter soil resources directly under their canopy, creating “islands” of fertility. We hypothesized that these two phases were associated with shrubs having different physiological response capacities related to their age or size and the resource structure of the environment. As a corollary, we hypothesized that responses of small shrubs would be more tightly coupled to variation in soil moisture availability compared to large shrubs. To test these hypotheses, we studied gas exchange and water relations of small (establishing) and large (established) shrubs growing in the Jornada del Muerto as a function of varying soil moisture during the season. The small shrubs had greater net assimilation, stomatal conductance, transpiration, and xylem water potential than large shrubs following high summer rainfall in July, and highest seasonal soil moisture at 0.3 m. High rates of carbon assimilation and water use would be an advantage for small shrubs competing with grasses when shallow soil moisture was plentiful. Large shrubs had greater net assimilation and water-use efficiency, and lower xylem water potential than small shrubs following a dry period in September, when soil moisture at 0.3 m was lowest. Low xylem water potentials and high water-use efficiency would allow large shrubs to continue acquiring and conserving water as soil moisture is depleted. Although the study provides evidence of differences in physiological responses of different-sized shrubs, there was not support for the hypothesis that small shrubs are more closely coupled to variation in soil moisture availability than large shrubs. Small shrubs may actually be less coupled to soil moisture than large shrubs, and thus avoid conditions when continued transpiration could not be matched by equivalent water uptake. 相似文献
235.
Ronghua Zhuge Siben Li Ter-Hsin Chen Walter H. Hsu 《Molecular reproduction and development》1995,41(1):20-28
This study investigated the underlying mechanisms of oxytocin (OT)-induced increases in intracellular Ca2+ concentrations ([Ca2+]i) in acutely dispersed myometrial cells from prepartum sows. A dosedependent increase in [Ca2+]i was induced by OT (0.1 nM to 1 μM) in the presence and absence of extracellular Ca2+ ([Ca2+]e). [Ca2+]i was elevated by OT in a biphasic pattern, with a spike followed by a sustained plateau in the presence of [Ca2+]e. However, in the absence of [Ca2+]e, the [Ca2+]i response to OT became monophasic with a lower amplitude and no plateau, and this monophasic increase was abolished by pretreatment with ionomycin, a Ca2+ ionophore. Administration of OT (1 μM) for 15 sec increased inositol 1,4,5-trisphosphate (IP3) formation by 61%. Pretreatment with pertussis toxin (PTX, 1 μg/ml) for 2 hr failed to alter the OT-induced increase in [Ca2+]i and IP3 formation. U-73122 (30 nM to 3 μM), a phospholipase C (PLC) inhibitor, depressed the rise in [Ca2+]i by OT dose dependently. U-73122 (3 μM) also abolished the OT-induced IP3 formation. Thapsigargin (2 μM), an inhibitor of Ca2+-ATPase in the endoplasmic reticulum, did not increase [Ca2+]i. However, it did time-dependently inhibit the OT-induced increase in [Ca2+]i. Nimodipine (1 μM), a Voltage-dependent Ca2+ channel (VDCC) blocker, inhibited the OT-induced plateau by 26%. La3+ (1 μM), a nonspecific Ca2+ channel blocker, abrogated the OT-induced plateau. In whole-cell patch-clamp studies used to evaluate VDCC activities, OT (0.1 μM) increased Ca2+ Current (Ica) by 40% with no apparent changes in the current-voltage relationship. The OT-induced increase in Ica reached the maximum in 5 min, and the increase was abolished by nimodipine (1 μM). These results suggested that (1) activation of OT receptors in porcine myometrium evokes a cascade in the PTX-insensitive G-protein–PLC-IP3 signal transduction, resulting in an increase in [Ca2+]i; (2) the OT-induced increase in [Ca2+]i is characterized by a biphasic pattern, in which the spike is predominately contributed by the intracellular Ca2+ release from the IP3-sensitive pool, and to a lesser extent by Ca2+ influx, whereas the plateau is from increased Ca2+ influx; and (3) the influx is via VDCC and receptor-operated Ca2+ channels. © 1995 Wiley-Liss, Inc. 相似文献
236.
Manfred Tacker Walter Fontana Peter F. Stadler Peter Schuster 《European biophysics journal : EBJ》1994,23(1):29-38
We present and study the behavior of a simple kinetic model for the melting of RNA secondary structures, given that those structures are known. The model is then used as a map that. assigns structure dependent overall rate constants of melting (or refolding) to a sequence. This induces a landscape of reaction rates, or activation energies, over the space of sequences with fixed length. We study the distribution and the correlation structure of these activation energies.
Correspondence to: P. Schuster 相似文献
237.
Walter J. Bock 《Journal of biosciences》1994,19(4):403-413
238.
J.K. Cowburn T. Goodall E.J. Fricker K.S. Walter C.R. Fricker 《Letters in applied microbiology》1994,19(1):50-52
Substrate specificities of proteases produced by two putrefactive marine bacteria, Shewanella putrefaciens and Alteromonas haloplanktis , were surveyed by using peptidyl-7-amino-4-methylcoumarin (MCA-substrates). Shewanella putrefaciens produced trypsin-like enzyme(s) showing broad spectrum specificity and chymotrypsin-like enzyme specifically hydrolysing Glt-Gly-Gly-Phe-MCA. Alteromonas haloplanktis produced high activity of ammopeptidase and trypsin-like enzyme(s) preferring Z-Phe-Arg-MCA, Bz-Arg-MCA and Boc-Leu-Ser-Thr-Arg-MCA. The two organisms would be able to utilize different proteins for their growth. 相似文献
239.
Christoph Meier Walter Senn Rudolf Hauser Manfred Zimmermanne 《Journal of mathematical biology》1994,32(6):563-572
The classical Nicholson-Bailey model for a two species host-parasitoid system with discrete generations assumes random distributions of both hosts and parasitoids, randomly searching parasitoids, and random encounters between the individuals of the two species. Although unstable, this model induced many investigations into more complex host-parasitoid systems. Local linearized stability analysis shows that equilibria of host parasitoid systems within the framework of a generalized Nicholson-Bailey model are generally unstable. Stability is only possible if host fertility does not exceede
4=54.5982 and if superparasitism is unsuccessful. This special situation has already been discovered by Hassell et al. (1983) in their study of the effects of variable sex ratios on host parasitoid dynamics. We discuss global behaviour of the Hassell-Waage-May model using KAM-theory and illustrate its sensitivity to small perturbations, which can give rise to radically different patterns of the population dynamics of interacting hosts and parasitoids. 相似文献
240.
Locus Heterogeneity for Waardenburg Syndrome is Predictive of Clinical Subtypes 总被引:5,自引:4,他引:1
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Lindsay A. Farrer Kathleen S. Arnos James H. Asher Clinton T. Baldwin Scott R. Diehl Thomas B. Friedman Jacquie Greenberg Kenneth M. Grundfast Christopher Hoth Anil K. Lalwani Barbara Landa Kate Leverton Aubrey Milunsky Robert Morell Walter E. Nance Valerie Newton Rajkumar Ramesar Valluri S. Rao Jennifer E. Reynolds Theresa B. San Agustin Edward R. Wilcox Ingrid Winship Andrew P. Read 《American journal of human genetics》1994,55(4):728-737
Waardenburg syndrome (WS) is a dominantly inherited and clinically variable syndrome of deafness, pigmentary changes, and distinctive facial features. Clinically, WS type I (WS1) is differentiated from WS type II (WS2) by the high frequency of dystopia canthorum in the family. In some families, WS is caused by mutations in the PAX3 gene on chromosome 2q. We have typed microsatellite markers within and flanking PAX3 in 41 WS1 kindreds and 26 WS2 kindreds in order to estimate the proportion of families with probable mutations in PAX3 and to study the relationship between phenotypic and genotypic heterogeneity. Evaluation of heterogeneity in location scores obtained by multilocus analysis indicated that WS is linked to PAX3 in 60% of all WS families and in 100% of WS1 families. None of the WS2 families were linked. In those families in which equivocal lod scores (between −2 and +1) were found, PAX3 mutations have been identified in 5 of the 15 WS1 families but in none of the 4 WS2 families. Although preliminary studies do not suggest any association between the phenotype and the molecular pathology in 20 families with known PAX3 mutations and in four patients with chromosomal abnormalities in the vicinity of PAX3, the presence of dystopia in multiple family members is a reliable indicator for identifying families likely to have a defect in PAX3. 相似文献