全文获取类型
收费全文 | 821篇 |
免费 | 66篇 |
出版年
2022年 | 3篇 |
2021年 | 12篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 16篇 |
2014年 | 24篇 |
2013年 | 34篇 |
2012年 | 44篇 |
2011年 | 30篇 |
2010年 | 28篇 |
2009年 | 36篇 |
2008年 | 47篇 |
2007年 | 41篇 |
2006年 | 45篇 |
2005年 | 47篇 |
2004年 | 34篇 |
2003年 | 37篇 |
2002年 | 28篇 |
2001年 | 36篇 |
2000年 | 25篇 |
1999年 | 29篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 13篇 |
1985年 | 17篇 |
1984年 | 8篇 |
1983年 | 12篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1967年 | 3篇 |
排序方式: 共有887条查询结果,搜索用时 15 毫秒
101.
Mörner T Eriksson H Bröjer C Nilsson K Uhlhorn H Agren E af Segerstad CH Jansson DS Gavier-Widén D 《Journal of wildlife diseases》2005,41(2):298-303
Ninety-eight brown bears (Ursus arctos), 20 gray wolves (Canis lupus), and 27 wolverines (Gulo gulo), all free-ranging, were submitted to the National Veterinary Institute, Uppsala, Sweden, during 1987-2001 for investigation of diseases and causes of mortality. The most common cause of natural death in brown bears was infanticide. Infanticide also was observed in wolverines but not in wolves. Traumatic injuries, originating from road or railway accidents, were the most common cause of death in wolves and occurred occasionally in brown bears. Most wolverines were submitted as forensic cases in which illegal hunting/poaching was suspected. Sarcoptic mange was observed in several wolves but not in brown bears or wolverines. Sarcoptic mange most likely was acquired from infected red foxes (Vulpes vulpes) that were killed by wolves. Other parasites and infectious diseases were only found sporadically. 相似文献
102.
Algesten G Sobek S Bergström AK Jonsson A Tranvik LJ Jansson M 《Microbial ecology》2005,50(4):529-535
We measured sediment production of carbon dioxide (CO2) and methane (CH4) and the net flux of CO2 across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were
made in situ under ambient light conditions. The flux of CO2 between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m−2 day−1 from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated
to dissolved organic carbon (DOC) concentration in the water (r2 = 0.61). The net flux of CO2 across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed
layer (r2 = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration.
Lakes with DOC concentrations <5.6 mg L−1 had net consumption of CO2 in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic
(<2.6 mg L−1) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In
addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water
column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources. 相似文献
103.
Ascorbic acid (vitamin C) induced hydrogen peroxide (H2O2) formation was measured in household drinking water and metal supplemented Milli-Q water by using the FOX assay. Here we show that ascorbic acid readily induces H2O2 formation in Cu(II) supplemented Milli-Q water and poorly buffered household drinking water. In contrast to Cu(II), iron was not capable to support ascorbic acid induced H2O2 formation during acidic conditions (pH: 3.5-5). In 12 out of the 48 drinking water samples incubated with 2 mM ascorbic acid, the H2O2 concentration exceeded 400 μM. However, when trace amounts of Fe(III) (0.2 mg/l) was present during incubation, the ascorbic acid/Cu(II)-induced H2O2 accumulation was totally blocked. Of the other common divalent or trivalent metal ions tested, that are normally present in drinking water (calcium, magnesium, zinc, cobalt, manganese or aluminum), only calcium and magnesium displayed a modest inhibitory activity on the ascorbic acid/Cu(II)-induced H2O2 formation. Oxalic acid, one of the degradation products from ascorbic acid, was confirmed to actively participate in the iron induced degradation of H2O2. Ascorbic acid/Cu(II)-induced H2O2 formation during acidic conditions, as demonstrated here in poorly buffered drinking water, could be of importance in host defense against bacterial infections. In addition, our findings might explain the mechanism for the protective effect of iron against vitamin C induced cell toxicity. 相似文献
104.
Oestrogen receptor β is present in both muscle fibres and endothelial cells within human skeletal muscle tissue 总被引:1,自引:1,他引:0
Wiik A Ekman M Morgan G Johansson O Jansson E Esbjörnsson M 《Histochemistry and cell biology》2005,124(2):161-165
Oestrogen receptor β (ERβ) is expressed in human skeletal muscle tissue. In the present study, we have developed an immunohistochemical
method to reveal if ERβ is located within the muscle fibres as well as within capillaries. Skeletal muscle biopsies were obtained
from m. quadriceps femoris vastus lateralis in four healthy young subjects. Immunohistochemical triple staining was applied
to transverse sections of paraffin-wax-embedded tissue. The basement membrane of muscle fibres and capillaries was identified
by using an antibody to collagen IV, endothelial cells using an antibody to CD34 and ERβ using a corresponding antibody. The
ERβ-positive (ERβ+) nuclei were located within the muscle fibre defined by the localisation of collagen IV. ERβ+ nuclei were
also, for the first time, found in endothelial cells of capillaries in skeletal muscle tissue. Quantification was performed
on transverse cryostat sections after performing a double staining (collagen IV and ERβ). It was shown that 24% of the ERβ+
nuclei were located within capillaries, and 76% were located within muscle fibres. In conclusion, ERβ in human skeletal muscle
tissue is expressed not only in the muscle fibres themselves, but also within the capillary endothelial cells. This observation
might improve understanding of the physiological role of oestrogen and its receptor. 相似文献
105.
106.
Jansson A Barnes E Klenerman P Harlén M Sørensen P Davis SJ Nilsson P 《Journal of immunology (Baltimore, Md. : 1950)》2005,175(3):1575-1585
We present a theoretical framework for simulating the synaptic accumulation of the costimulatory molecules CD28, CTLA-4, B7-1, and B7-2, based on a system of mean-field, ordinary differential equations, and rigorous biophysical and expression data. The simulations show that binding affinity, stoichiometric properties, expression levels, and, in particular, competition effects all profoundly influence complex formation at cellular interfaces. B7-2 engages 33-fold more CD28 than CTLA-4 at the synapse in contrast to B7-1, which ligates approximately 7-fold more CTLA-4 than CD28. Although B7-1 completely dominates interactions with CTLA-4, forming linear arrays of 7-18 receptor-ligand pairs, CTLA-4 is fully engaged by B7-2 when B7-1 is absent. Additional simulations reveal the sensitivity of CD28 interactions to modeled transport processes. The results support the concept that B7-2 and B7-1 are the dominant ligands of CD28 and CTLA-4, respectively, and indicate that the inability of B7-2 to recruit CTLA-4 to the synapse cannot be due to the differential binding properties of B7-1 and B7-2 only. We discuss the apparent redundancy of B7-1 in the context of a potentially dynamic synaptic microenvironment, and in light of functions other than the direct enhancement of T cell inhibition by CTLA-4. 相似文献
107.
Stefan Jansson Ivar Virgin Petter Gustafsson Bertil Andersson Gunnar Öqulst 《Physiologia plantarum》1992,84(1):6-12
Both chlorophyll a and b and polypeptides of the photosynthetic apparatus are found in gymnosperm seedlings. germinated and grown in absolute darkness. The photosystem II (PSII) activity is, however, limited, probably due to an inactive oxygen evolving system. In the present study dark-grown seedlings of Scots pine ( Pinus sylvestris L.) were transferred to light and changes in antenna size and the activation process of PSII were investigated using fluorescence measurements and quantitative western blotting. It was found that the activation process is rapid, requires very little light and that strong light inhibits the process. It takes place without any changes in the primary reactions of PSII. Furthermore, all polypeptides except the major light-harvesting chlorophyll a/b -binding protein complex of PSII (LHCII) were present in dark-grown seedlings in amounts comparable to the light treated control. The dark-grown seedlings had the same LHCII polypeptide composition as light treated seedlings, and the LHCII present seemed to be fully connected to the reaction centre. The results indicate that activation of PSII in dark-grown conifer seedlings resembles the photoactivation process of angiosperms. This implies that the fundamental processes in the assembly of the photosystem II complex is the same in all plants, but that the regulation differs between different taxa. 相似文献
108.
109.
Caspases are essential in animal programmed cell death both as initiator and executioner proteases. Plants do not have close caspase homologues, but several instances of caspase-like proteolytic activity have been demonstrated in connection with programmed cell death in plants. It was asked if caspase-like proteases are involved during development of the barley caryopsis. The presence of a caspase-6-like proteolytic activity that preferentially cleaved the sequence VEID was demonstrated. A range of protease inhibitors was tested and only caspase-specific inhibitors showed major inhibitory effects. The profile of VEIDase activity in developing starchy endosperm, embryo, and whole caryopsis was measured and showed a general trend of higher activity in young, rapidly developing tissues. The VEIDase activity was localized in vivo to vesicles, shown to be autophagosomes, in randomly distributed cells of the starchy endosperm. The VEIDase activity detected in barley caryopsis is similar to activities described previously in mammals, spruce, yeast, and thale cress. In mammals, spruce, and yeast, VEIDase activity has been shown to be positively correlated with the occurrence of programmed cell death. Several manifestations of programmed cell death exist in developing barley caryopsis, indicating a connection between VEIDase activity and developmental programmed cell death in barley. 相似文献
110.
Bylesjö M Sjödin A Eriksson D Antti H Moritz T Jansson S Trygg J 《Bioinformatics (Oxford, England)》2006,22(20):2554-2555
MASQOT-GUI provides an open-source, platform-independent software pipeline for two-channel microarray spot quality control. This includes gridding, segmentation, quantification, quality assessment and data visualization. It hosts a set of independent applications, with interactions between the tools as well as import and export support for external software. The implementation of automated multivariate quality control assessment, which is a unique feature of MASQOT-GUI, is based on the previously documented and evaluated MASQOT methodology. Further abilities of the application are outlined and illustrated. AVAILABILITY: MASQOT-GUI is Java-based and licensed under the GNU LGPL. Source code and installation files are available for download at http://masqot-gui.sourceforge.net/ 相似文献