全文获取类型
收费全文 | 4038篇 |
免费 | 401篇 |
国内免费 | 3篇 |
专业分类
4442篇 |
出版年
2023年 | 27篇 |
2022年 | 56篇 |
2021年 | 95篇 |
2020年 | 77篇 |
2019年 | 104篇 |
2018年 | 101篇 |
2017年 | 108篇 |
2016年 | 125篇 |
2015年 | 207篇 |
2014年 | 193篇 |
2013年 | 278篇 |
2012年 | 288篇 |
2011年 | 299篇 |
2010年 | 152篇 |
2009年 | 142篇 |
2008年 | 229篇 |
2007年 | 200篇 |
2006年 | 183篇 |
2005年 | 173篇 |
2004年 | 176篇 |
2003年 | 171篇 |
2002年 | 140篇 |
2001年 | 93篇 |
2000年 | 71篇 |
1999年 | 95篇 |
1998年 | 52篇 |
1997年 | 44篇 |
1996年 | 35篇 |
1995年 | 23篇 |
1994年 | 31篇 |
1993年 | 28篇 |
1992年 | 37篇 |
1991年 | 32篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 34篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 15篇 |
1983年 | 14篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1974年 | 19篇 |
1973年 | 11篇 |
1972年 | 9篇 |
排序方式: 共有4442条查询结果,搜索用时 15 毫秒
981.
P. Mariani Franco Rustichelli Letizia Saturni Lorenzo Cordone 《European biophysics journal : EBJ》1999,28(4):294-301
Trehalose is known to protect some organisms from various stresses due to drought and high temperature. To explore the molecular
mechanism of the protective function, the mesomorphic properties of the monoolein-water system, dried in the presence of trehalose,
were studied by X-ray diffraction. While, in pure water, two bicontinuous inverse cubic structures (the Pn3m and Ia3d phases) and a lamellar Lα phase exist as a function of concentration, only the Pn3m cubic phase has been detected in concentrated trehalose solutions or in trehalose glasses, even under extremely dry conditions.
Depending on the sugar concentration, or after glass dehydration, the Pn3m cubic unit cell decreases to very low values, much below the smaller one observed in pure water. However, as no phase transitions
occur, a simple osmotic mechanism can be excluded. An additional stabilization of the lipid phase, arising from interfacial
free energy changes due to trehalose-water-lipid direct interactions, and large enough to affect the energetic balance between
the Pn3m and the Ia3d cubic phases, evidently occurs. Moreover, no differences in the Pn3m cubic structure were observed when the sugar platelets convert to the glassy state; no apparent structural modifications
that can be related to mechanical pressure exerted on the lipid phase have been detected.
Received: 5 October 1998 / Accepted: 13 November 1998 相似文献
982.
P Gauthier C Gottesmann 《Comptes rendus des séances de la Société de biologie et de ses filiales》1975,169(6):1589-1592
21 subjects were recorded during two experimental sessions: 1st session: 2 CNVs in control conditions; 2nd session: 1) control CNV, 2) CNV and arithmetic calculation, 3) CNV and labyrinthine stimulation, 4) CNV, arithmetic calculation and labyrinthine stimulation, 5) control CNV. The results obtained show a post-imperative extension of the CNV in the situation 2: arithmetic calculation (P less than 0.025) and 4: double interference (P less than 0.05). 相似文献
983.
Jian Zhong Tong Sophie Sarrazin Doris Cassio Frdric Gauthier Fernando Alvarez 《Biology of the cell / under the auspices of the European Cell Biology Organization》1994,81(1):77-81
Summary— Human hepatocytes cultured with a hormonally defined medium on non-adherent poly-(2-hydroxyethyl methacrylate) coated surface were able to form spheroids. The maintenance of liver-specific functions was assessed by following secretion of albumin, transferrin and α-antitrypsin that were still detectable after 4 months of spheroidal culture. Moreover, cytochrome P-450 IA was induced by methylcholanthrene for up to 2 weeks. This cell system is very promising for long-term in vitro studies of human hepatocyte functions. 相似文献
984.
J. C. Lorenzo E. Ojeda A. Espinosa Carlos Borroto 《In vitro cellular & developmental biology. Plant》2001,37(6):803-806
Summary The temporary immersion bioreactor has been found to be an important tool for sugarcane micropropagation, allowing higher
shoot formation rates and cost reduction. This research was conducted to demonstrate the agricultural value of temporary immersion
bioreactor-derived sugarcane plants. The experiment was carried out for about 2 yr to study the field performance of these
plants. Two control treatments were also evaluated representing the conventional forms of micro- and macropropagation. Growth
of sugarcane stools, first ratoon and the use of micropropagated plants for macropropagation were recorded. Some botanical
and chemical characteristics were evaluated. Differences among propagation systems were only found in the first 6 mo. of field
growth, regarding the stem length and diameter. Such differences disappeared with the course of the experiment. 相似文献
985.
The conjugative transfer of plasmid RP4 between two strains of Escherichia coli in a sterile marine sediment was enhanced by the presence of glycine betaine (frequency increased 20 to 40 times). The conjugation was also facilitated by the osmoprotection of donor cells. Glycine betaine is a universal osmolyte and has been found in marine sediments at high concentrations. So this phenomenon could have epidemiological and sanitary importance by increasing the possibility of dissemination of some plasmids present in enterobacteria in natural marine deposits. 相似文献
986.
987.
988.
G Atienza M Aldegunde J A Veira A Lorenzo R Conejero 《Revista Espanola de Fisiología》1989,45(1):15-20
Some serum and brain amino acid variations occurring in animals with short term streptozotocin-diabetes (24 h) are studied in this work. Diabetic animals showed an increase in serum of the three branched-chain amino acids as well as an increase in free tryptophan, besides a decrease in total serum tryptophan and in the tryptophan/competitor amino acids ratio. In brain, the three branched-chain amino acids increased, but there were no variation in whole brain tryptophan. Nevertheless, by studying levels of tryptophan in different brain regions, an increase in medulla-pons was recorded. This circumstance could be explained by the increase in free serum tryptophan levels, in agreement with several authors who assign this reason for brain tryptophan. 相似文献
989.
990.
A replicate haul experiment was carried out using the verticallytowed PAIROVET net in an area of high abundance of anchovy eggsin the Bay of Biscay. The main aim of the experiment was tocompare the performance of ships of different size working inthe same area. In addition, we tested the performance of thePAIROVET net and the deployment methodology used to sample anchovyeggs for biomass assessment purposes. We concluded that underthe experimental conditions experienced in this cruise, differentships yield similar performances of the vertically towed PAIROVETnet if the methodology is kept similar. The ANOVA suggests thatthe systematic central sampling (SCS) scheme currently in usefor the Bay of Biscay anchovy biomass estimations (one stationout at 3 miles) adequately represents the surrounding area alongthe transect line. The among-station component of variance withinthe unit sampling area of the current SCS turned out to be comparableand, in some cases, smaller than the within-station variance.Consequently, the spatial design of the SCS adopted during routinesurveys appears to be a reliable strategy for sampling anchovyeggs in areas of high egg abundance, as in this experiment.In addition, it ensures fairly independent data units. In thearea of the experiment, the most disperse egg stages (like 2-and 3-day-old eggs) show a larger within-station component ofvariance than the spatial component of variance within the rectanglesof the current SCS. This suggests that for these stages, thesampling can still be improved cheaply by increasing the precisionof egg abundance estimates per station with larger sample sizes,without changing the spatial sampling scheme or the number ofstations. However, the benefits of this strategy will hardlyaffect the precision of the 1-day-old egg estimates becauseof their patchy distribution. 相似文献