全文获取类型
收费全文 | 717篇 |
免费 | 63篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 18篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 30篇 |
2014年 | 32篇 |
2013年 | 33篇 |
2012年 | 48篇 |
2011年 | 48篇 |
2010年 | 34篇 |
2009年 | 33篇 |
2008年 | 36篇 |
2007年 | 34篇 |
2006年 | 36篇 |
2005年 | 26篇 |
2004年 | 39篇 |
2003年 | 44篇 |
2002年 | 28篇 |
2001年 | 15篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 23篇 |
1997年 | 6篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有780条查询结果,搜索用时 15 毫秒
761.
Pekka Lähdesmäki Tuulikki Pakonen Esko Saari Kari Laine Leena Tasanen Paavo Havas 《Ecography》1990,13(1):31-38
Free amino acids and related compounds together with total nitrogen, total protein and soluble small-molecular nitrogen were analyzed quantitatively in monthly tissue samples from bilberry, Vaccinium myrtillus , from 15 May to 24 September 1985, in Oulu, northern Finland. Pronounced accumulation (at the millimolar level) of soluble low-molecular-weight nitrogen in the form of free amino acids was observed at the end of September. Arginine in particular accumulated in the rhizomes and older branches. Protein levels remained relatively constant. Mobilization of amino acids from winter storage into the growing tissues (buds) was evident in May. 相似文献
762.
Synopsis The histochemical digestability with neuraminidase of sialomucin in mouse sublingual gland was studied in unfixed and formaldehyde vapour-fixed cryostat sections, and in sections prepared from paraffin-embedded material fixed in several alcohol- or formaldehyde-containing fixatives recommended for mucosubstances.The removal of sialic acid residues from sections treated with neuraminidase was followed histochemically with the following staining methods: Azure A pH 3.5, Alcian Blue pH 2.5, Low Iron Diamine and Alcian Blue pH 2.5 followed by periodic acid-Schiff. When Goland's methanolic cyanuric chloride was used as fixative, only a partial loss of tissue basophilia was evident after enzyme incubation, but in tissues fixed in other ways a complete loss of histochemically detectable sialic acid residues was observed. 相似文献
763.
764.
Aim Species–area relationships are often applied, but not generally approved, to guide practical conservation planning. The specific species group analysed may affect their applicability. We asked if species–area curves constructed from extensive databases of various sectors of natural resource administration can provide insights into large‐scale conservation of boreal forest biodiversity if the analyses are restricted only to red‐listed species. Location Finland, northern Europe. Methods Our data included 12,645 records of 219 red‐listed Coleoptera and Fungi from the whole of Finland. The forest data also covered the entire country, 202,761 km2. The units of species–area analyses were 224 municipalities where the red‐listed forest species have been observed. We performed a hierarchical partitioning analysis to reveal the relative importance of different potential explanatory variables. Based on the results, for all red‐listed species, species associated with coniferous trees and for Fungi, the area of economically over‐aged forests explained the best the variation in data. For species associated with deciduous trees and Coleoptera, the forest area explained better variation in data than the area of old forests. In the subsequent log–log species–area regression analyses, we used the best variables as the explanatory variable for each species group. Results There was a strong relationship between the number of all red‐listed species and the area of old forests remaining, with a z‐value of 0.45. The area explained better the number of species associated with conifer trees and Fungi than the number of species associated with deciduous trees and Coleoptera. Main conclusions The high z‐values of species–area curves indicate that the remaining old‐growth patches constitute a real archipelago for the conifer‐associated red‐listed species, since lower values had been expected if the surrounding habitat matrix were a suitable habitat for the species analysed. 相似文献
765.
Pekka Vilkamaa 《Systematic Entomology》2000,25(1):47-72
The phylogeny of Phytosciara Frey, Prosciara Frey, Dolichosciara Tuomikoski (together forming Phytosciara sensu Tuomikoski), Lobosciara Steffan and Bradysia Winnertz was studied by parsimony analysis using the computer programs Pee‐Wee and NONA. The analysis was based on sixty‐four morphological characters from adult males, coded for thirty‐nine ingroup and two outgroup terminals. Three cladograms of the maximum fit (Pee‐Wee) and one of the minimum length (NONA) were obtained, some of them with polytomies. Many characters showed much homoplasy in the cladograms. The solution by the fittest cladograms was chosen as the main hypothesis of the phylogeny. Of the groups studied, only Lobosciara appeared monophyletic. The relationships of the taxa in their now revised monophyletic sense are: Dolichosciara + (Lobosciara + ((‘Prosciara’ fuscina group + ‘P’. vulcanata) + (‘P’. mima group + ((‘P’. perfida + (Bradysia + Phytosciara)) + Prosciara)))). Phytosciara Frey, Prosciara, Dolichosciara and Lobosciara in their revised concepts are regarded as genera. 相似文献
766.
Transfer RNAs for glycine, proline, lysine, serine and leucine were compared in developing rat granulation tissue 6 and 15 days after sterile subcutaneous implantation of pieces of cellulose sponge. The acceptance of glycine, proline and lysine by unfractionated tRNAs were ca. 30 per cent greater in tRNA derived from 15-day granulation tissue, whereas those of serine and leucine were unaltered. Cochromatography on benzoylated DEAE-cellulose of the 3H- and 14C-labeled aminoacyl-tRNAs from the two sources revealed a significant increase in the relative amount of one of the three glycyl-tRNA fractions in the 15-day granulation tissue, whereas the elution profiles for prolyl-, lysyl-, seryl-, and leucyl-tRNAs were unaltered. The changes observed suggest a causal relation to the enhanced synthesis of collagen in the late-stage granulation tissue. 相似文献
767.
Regulation of the Cortical Actin Cytoskeleton in Budding Yeast by Twinfilin,a Ubiquitous Actin Monomer-sequestering Protein 下载免费PDF全文
Here we describe the identification of a novel 37-kD actin monomer binding protein in budding yeast. This protein, which we named twinfilin, is composed of two cofilin-like regions. In our sequence database searches we also identified human, mouse, and Caenorhabditis elegans homologues of yeast twinfilin, suggesting that twinfilins form an evolutionarily conserved family of actin-binding proteins. Purified recombinant twinfilin prevents actin filament assembly by forming a 1:1 complex with actin monomers, and inhibits the nucleotide exchange reaction of actin monomers. Despite the sequence homology with the actin filament depolymerizing cofilin/actin-depolymerizing factor (ADF) proteins, our data suggests that twinfilin does not induce actin filament depolymerization. In yeast cells, a green fluorescent protein (GFP)–twinfilin fusion protein localizes primarily to cytoplasm, but also to cortical actin patches. Overexpression of the twinfilin gene (TWF1) results in depolarization of the cortical actin patches. A twf1 null mutation appears to result in increased assembly of cortical actin structures and is synthetically lethal with the yeast cofilin mutant cof1-22, shown previously to cause pronounced reduction in turnover of cortical actin filaments. Taken together, these results demonstrate that twinfilin is a novel, highly conserved actin monomer-sequestering protein involved in regulation of the cortical actin cytoskeleton. 相似文献
768.
Four intact and four parathyroidectomized rats, fed with a low calcium diet, were treated with progesterone, 0.7 mg s.c. daily on four consecutive days, and the effects of the treatment on the serum calcium and inorganic phosphorus were investigated. Four untreated intact rats on the same diet served as controls. The treatment was found to have no influence on the concentrations of the serum calcium or inorganic phosphorus. 相似文献
769.
Pekka Pamilo 《Evolution; international journal of organic evolution》1990,44(3):689-697
Methods used for estimating the confidence levels of UPGMA-type phenograms based on molecular-genetic data are examined. The methods based on internodal variances or on bootstrapping over characters are compared by simulating a three-species phylogeny with a trifurcation. The bootstrap method seems slightly better in this comparison. Weighting of OTU's when constructing the phenogram is also examined. A method that weights each OTU according to the estimated independent evolutionary information, a modified WPGMA, appears slightly better than UPGMA in estimating the branching points and branch lengths. The methods are applied to the data on restriction sites in eight Hawaiian Drosophila species. The significance of the clusters among them differ from those reported earlier. 相似文献
770.
Fractionation of mouse T and B lymphocytes by preparative cell electrophoresis. Efficiency of the method 总被引:6,自引:0,他引:6
Mouse lymphocytes have been fractionated in preparative cell electrophoresis into two functionally viable populations, a high mobility cell (HMC) and a low mobility cell (LMC) population. The distribution of HMC in CBA spleen, blood, and lymph node corresponds to known proportions of θ-positive cells in these organs. The HMC carry the θ-isoantigen, respond to phytohemagglutinin in vitro, and induce a graft-versus-host reaction in newborn F1 hybrid mice. Nearly all spleen LMC have complement receptors on their surface. About 70% of spleen LMC are sensitive to anti-MBLA serum and form “caps” when incubated with FITC-conjugated anti-Ig. Only LMC respond to E. coli lipopolysaccharide. Thus, T cells localize in the HMC population and B cells in the LMC population. There is no detectable contamination of T lymphocytes among the LMC, nor of B lymphocytes among the HMC. 相似文献