全文获取类型
收费全文 | 2756篇 |
免费 | 383篇 |
国内免费 | 1691篇 |
出版年
2024年 | 55篇 |
2023年 | 178篇 |
2022年 | 185篇 |
2021年 | 220篇 |
2020年 | 212篇 |
2019年 | 218篇 |
2018年 | 185篇 |
2017年 | 188篇 |
2016年 | 203篇 |
2015年 | 189篇 |
2014年 | 226篇 |
2013年 | 249篇 |
2012年 | 215篇 |
2011年 | 223篇 |
2010年 | 161篇 |
2009年 | 213篇 |
2008年 | 197篇 |
2007年 | 222篇 |
2006年 | 184篇 |
2005年 | 135篇 |
2004年 | 134篇 |
2003年 | 112篇 |
2002年 | 118篇 |
2001年 | 79篇 |
2000年 | 60篇 |
1999年 | 64篇 |
1998年 | 52篇 |
1997年 | 34篇 |
1996年 | 38篇 |
1995年 | 39篇 |
1994年 | 35篇 |
1993年 | 30篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1958年 | 1篇 |
排序方式: 共有4830条查询结果,搜索用时 0 毫秒
11.
The degree of intergradation between two species of Sulawesi macaques,Macaca tonkeana andM. hecki, was studied by examining the diagnostic external characteristics of more than 100 monkeys kept as pets by natives. Two possible
hybrid monkeys were found and both originated from the borderland between the two species, located in the most proximal region
of the northern peninsula of Sulawesi. The previously postulated wide area of integradation between the two species at the
possible contact zone was, however, not recognized, and typical examples oftonkeana orhecki were found to be present on the two sides of a narrow “hybrid” zone which was defined by direct observations. Furthermore,
despite considerable individual variations, we were able to allocate most monkeys to one or other of the species. Each of
ten external characteristics of the members of both species more or less encompassed the individual variations, but may undergo
changes with the development of the monkeys. The mechanisms of reproduction of hybrid monkeys and the maintenance of differences
between the species are discussed. 相似文献
12.
Kunio Watanabe Shuichi Matsumura Tsuyoshi Watanabe Yuzuru Hamada 《Primates; journal of primatology》1991,32(3):385-389
Morphological observations of pet and wild monkeys were made in the area that was inferred to be the borderland betweenMacaca tonkeana andM. ochreata in Sulawesi. Almost all individual monkeys could be classified into one of two species by their external characteristics.
The possible borderland was estimated to extend from the La River in the east and to around Karaena River in the west. These
two species may make contact in the forest in the western area of the borderland. Some external characteristics exhibited
wide individual variations in the two species. Some monkeys originating from the borderland showed external characteristics
that were intermediate between those of the two species. The possible intergradation between these two species is discussed
in terms of the morphological variations found in the two species. 相似文献
13.
14.
Hendrica A. Akster 《Cell and tissue research》1985,241(1):193-201
Summary Ultrastructural parameters of muscle fibre types of the carp (Cyprinus carpio L.) were measured and compared with their contractile properties. In red fibres, which are slower than pink fibres, the relative length of the junction between the T system and the sarcoplasmic reticulum (T-SR junction) is smaller and the Z lines are thicker than in pink fibres. Pink fibres have a smaller relative length of T-SR junction than white fibres from the axial muscles. The two types of red fibres present in carp muscle also differ in their relative lengths of T-SR junction. Significant differences in the relative areas of the SR were not found.The relative volume of myofibrils in red fibres is two-thirds that in pink fibres, a difference that is not reflected in the maximal isometric tetanic tensions of these types. Red fibres, which are less easily fatigued than pink fibres, have larger relative volumes of subsarcolemmal and intermyofibrillar mitochondria. Small pink fibres have a larger relative volume of subsarcolemmal mitochondria than large pink fibres, but have a similar relative volume of intermyofibrillar mitochondria. Small and large pink fibres differ in the relative volumes of their membrane systems, but have similar relative lengths of T-SR junction. 相似文献
15.
The properties and sources of all known endonucleases and methylases acting site-specifically on DNA are listed. The enzymes are crossindexed (Table I), classified according to homologies within their recognition sequences (Table II), and characterized within Table II by the cleavage and methylation positions, the number of recognition sites on the DNA of the bacteriophages lambda, phi X174 and M13mp7, the viruses Ad2 and SV40, the plasmids pBR322 and pBR328 and the microorganisms from which they originate. Other tabulated properties of the restriction endonucleases include relaxed specificities (Table III), the structure of the restriction fragment ends (Table IV), and the sensitivity to different kinds of DNA methylation (Table V). Table VI classifies the methylases according to the nature of the methylated base(s) within their recognition sequences. This table also comprises those restriction endonucleases, which are known to be inhibited by the modified nucleotides. Furthermore, this review includes a restriction map of bacteriophage lambda DNA based on sequence data. Table VII lists the exact nucleotide positions of the cleavage sites, the length of the generated fragments ordered according to size, and the effects of the Escherichia coli dam- and dcmI-coded methylases M X Eco dam and M X Eco dcmI on the particular recognition sites. 相似文献
16.
Recent molecular biological, chemical, physiological and morphological studies indicate that Trichosporon cutaneum and related species should be reclassified. In this study, antigenic characteristics of the species were determined. The results of adsorption experiments revealed that there were at least three serological types: I, II and III. Specific factor sera I, II and III were prepared on the basis of adsorption experiments and isolates were serotyped by cell slide agglutination (CSA). Since the CSA test was difficult to read in some strains, the results of the CSA test were compared with the findings from an enzyme-linked immunosorbent assay (ELISA). For the ELISA, crude polysaccharide antigens prepared from the culture supernatant were used as the antigen. The types determined by ELISA correlated well with those determined by the CSA test. These data suggest that T. cutaneum and related species have at least three serological types, and that the typing can be done by either CSA or ELISA. 相似文献
17.
露水草的光合特性及其生态学意义 总被引:2,自引:0,他引:2
用盆栽和遮阴试验研究了露水草(Cyanotis arachnoidea Clarke) 的光合作用特征,比较了不同遮光水平对光合速率、光合器官特性及光合产量的影响。结果如下:1.露水草是一种耐阴偏阳的C3 类草木植物,其光合作用的光饱和点约为650 μm ol·m - 2·s- 1,光补偿点约为17 μm ol·m - 2·s- 1,且具有高达130×10- 6的CO2 补偿点。2.露水草的最大净光合速率为12.45 μm ol·m - 2·s- 1。叶片净光合速率的日变化规律呈双峰曲线,主峰在11~12 时,次峰在15时左右。3.遮光20% ~50% 有利于露水草的生长。与对照相比,叶片中叶绿素b 的含量增加了47% ~83% ,并且由于净光合速率(相对光合速率)的提高,使光合生产量增加了12% ~18% 。 相似文献
18.
马桑菌株的生物学特性 总被引:3,自引:0,他引:3
对从湖北、四川、云南等地采集的尼泊尔马桑(Coriaria nepalensis Wall.)根瘤中分离的20株内生菌纯培养物所进行的研究表明,其形态均具有弗兰克氏菌属的特征。在粗细不一的分枝菌丝体上有泡囊和孢囊,有的还有串珠状结构的菌丝体。不同菌株在液体培养基上生长速度很不一致;菌丝体多呈絮状或颗粒状沉淀,个别还呈薄膜状沉淀;绝大多数菌株的菌丝体具有不同色调的色素;在S培养基中大多数都能产生可溶性色素。上述这些培养特征常因培养基成分和培养方式的不同而有差异。大多数菌株的胞壁组分属Ⅱ型,少数菌株为Ⅲ型;全细胞糖型变化很大,20个菌株可划分为6个糖型,而且绝大多数糖型与已知弗兰克氏菌有所不同。此外,有65%的菌株还具有明显的抗菌活性。 相似文献
19.
Analysis of the multi-stem clump structure ofLitsea japonica Juss. growing in a coastal dwarf forest
The multi-stem clump structure of a coastal dwarf forest dominated byLitsea japonica Juss. was investigated in order to clarify the sprouting characteristics and self-maintenance of clumps by stem alternation.
The size and age distribution of multi-stem clumps were analyzed using cumulative relative frequency curves.L. japonica had a large number of stems and an even height distribution or young age-biased distribution of stems within a clump. These
results indicated the sequential flushing of sprouts at high frequency. Height distribution within a clump ofL. japonica was relatively even compared to other species. This clump structure suggested the stable self-maintenance of individuals
in all ranges of size and age without disturbances. It originated specific sprouting characteristics as a response to the
severe stress of salty wind.Ardisia sieboldii Miq. had few stems within a clump. Although the stem height distribution of large individuals tended to be even, most clumps
had a large size-biased distribution of stem height which indicated simultaneous sprouting. From this structure, sprouts of
this species were thought to be of less significance in the stable self-maintenance of individuals thanL. Japonica. 相似文献
20.