全文获取类型
收费全文 | 2411篇 |
免费 | 121篇 |
出版年
2023年 | 11篇 |
2022年 | 15篇 |
2021年 | 55篇 |
2020年 | 29篇 |
2019年 | 45篇 |
2018年 | 52篇 |
2017年 | 48篇 |
2016年 | 78篇 |
2015年 | 98篇 |
2014年 | 118篇 |
2013年 | 137篇 |
2012年 | 203篇 |
2011年 | 190篇 |
2010年 | 121篇 |
2009年 | 112篇 |
2008年 | 172篇 |
2007年 | 122篇 |
2006年 | 124篇 |
2005年 | 131篇 |
2004年 | 128篇 |
2003年 | 107篇 |
2002年 | 99篇 |
2001年 | 19篇 |
2000年 | 24篇 |
1999年 | 49篇 |
1998年 | 18篇 |
1997年 | 18篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 17篇 |
1991年 | 16篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1966年 | 5篇 |
排序方式: 共有2532条查询结果,搜索用时 425 毫秒
21.
22.
Takuya Kajimoto 《Ecological Research》1989,4(1):55-69
Aboveground biomass and litterfall ofPinus pumila scrubs, growing on the Kiso mountain range in central Japan, were investigated from 1984 to 1985. The biomass of two research
plots (P1 and P2) with different scrub heights was estimated by two methods, the stratified clip technique and the allometric
method. Aboveground total biomass estimated by the latter method reached 181 ton d.w. ha−1 in P1 and 132 ton d.w. ha−1 in P2. Creeping stems contributed to about half of the total biomass. Although estimates of woody organs differed between
the two plots, leaf biomass estimates were almost the same at 15.5 ton d.w. ha−1. The canopies of the twoP. pumila scrubs were characterized by a large mean leaf area density of 5.0 m2 m−3. Despite this large area density, relatively moderate attenuation of light intensity was observed. Specific leaf area generally
increased with reduced leaf height. Annual total litterfall was estimated to be 3.60 ton d.w. ha−1 yr−1 in P1 and 2.39 ton d.w. ha−1 yr−1 in P2. Annual leaf fall in both plots was approximately 2.0 ton d.w. ha−1 yr−1. Leaves fell mainly in early autumn. Annual loss rates of branches, estimated as the sum of annual branch litterfall and
the amount of newly formed attached dead branches, were 0.29 ton d.w. ha−1 yr−1 in P1 and 0.37 ton d.w. ha−1 yr−1 in P2. 相似文献
23.
We examined the developmental ability of enucleated eggs receiving embryonic nuclei and male primordial germ cells (PGCs) in the mouse. Reconstituted eggs developed into the blastocyst stage only when an earlier 2-cell nucleus was transplanted (36%) but very rarely if the donor nucleus was derived from a later 2-cell, 8-cell, or inner cell mass of a blastocyst (0-3%). 54-100%, 11-67%, 6-43% and 6-20% of enucleated eggs receiving male PGCs developed to 2-cell, 4-cell, 8-cell and blastocyst stage, respectively, in culture. The overall success rate when taking into account the total number of attempts at introducing germ cells was actually 0-6%. Live fetuses were not obtained after transfer of reconstituted eggs to recipients, although implantation sites were observed. The developmental ability of reconstituted eggs in relation to embryonic genome activation and genomic imprinting is discussed. 相似文献
24.
Endotoxic properties of chemically synthesized lipid A analogs. Studies on six inflammatory reactions in vivo, and one reaction in vitro 总被引:1,自引:0,他引:1
M Yoshida M Hirata K Inada N Tsunoda T Kirikae T Onodera Y Ishikawa O Sasaki T Shiba S Kusumoto 《Microbiology and immunology》1989,33(10):797-810
Biological activities of two groups of synthesized lipid A analogs, the counterpart of biosynthetic precursor, Lehmann's Ia type, 406, and E. coli lipid A type, 506, as well as their non-phosphorylated, and mono-phosphorylated analogs were investigated. The activities employed included four bone marrow cell reactions in mice, mice skin reaction, leukocytes migration in rabbits' cornea, and hemagglutination. Compound 406 and 506 elicited bone marrow reactions in mice and hemagglutination of mouse RBC, although 406 failed to elicit hemorrhage and necrosis also in mice skin. Compound 406 did not elicit corneal reaction in rabbits. The results suggest that for elicitation of this reaction and mice skin reaction, acyloxyacyl structure is required. Cytotoxicity and thromboplastin production of four bone marrow reactions had been reported by us to be endotoxic reactions, since these had not been elicited by peptidoglycan of Lactobacillus and Staphylococcus (1981) and 300 series synthesized analogs (1984) which did not have endotoxic structures. From these results, it seems that these two marrow reactions and hemagglutination require, as does the limulus test, the lipid A part structure as is present in 406. 相似文献
25.
Hiroyuki Tsunoda Toshio Ohshima Jun Tohyama Masayuki Sasaki Norio Sakuragawa Frank Martiniuk 《Human genetics》1996,97(4):496-499
We report a missense mutation in an adult Japanese patient with acid alpha-glucosidase (GAA) deficiency. A TC to GT transition
at nucleotides 1585–1586, was identified. This transition resulted in an amino acid substitution of Ser-529 to Val (S529V)
in exon 11. We also have demonstrated that the S529V mutation abolishes the catalytic activity of the enzyme. Our data suggest
that this mutation is the cause of the clinical manifestation known as adult-onset GAA deficiency. The missense mutation described
here is a new mutation, and the first identified in Japanese patients with GAA deficiency.
Received: 23 May 1995 相似文献
26.
Different numbers of CD-1 mouse zygotes(1, 5, 10, 20, 40 and 60) were cultured in 10 mul M16 medium, in M16 medium+EDTA, in M16 dedium+SOD+thioredoxin, and in CZB medium, respectively. When the zygotes, regardless of the number, were cultured with M16, no blastocysts could be obtained. The suitable ratio of embryos to 1 mul of M16 medium+EDTA or M16 medium+SOD+thioredoxin was 1:1 or 2:1. Medium volume from 1 to 10 mul did not affect blastocyst development when the embryo density was 1:1. However, blastocysts obtained from zygotes cultured singly had fewer cell numbers and showed inferior development to live fetuses after transfer to recipients. When CZB medium was used, suitable embryo density was not clear. The ratio of embryos to volume of culture medium was shown to be an important factor for in vitro culture of mouse zygotes. 相似文献
27.
Experiments were conducted to test the hypothesis that the nucleo/cytoplasmic ratio of mouse embryos determines the time of blastocele formation. Half the volume of 2-cell stage embryos was removed from each blastomere by micropipette to alter the nucleo/cytoplasmic ratio. Reduced embryos whose nucleo/cytoplasmic ratio increased and non-treated control embryos were cultured in vitro to compare the timing of division to the 4-cell stage and blastocele formation. Reduced 2-cell embryos formed blastoceles significantly earlier than the controls (49.0 +/-2.9 vs 52.2 +/-6 h) and with fewer cells, although division into the 4-cell stage was significantly delayed (11.4 +/-4.4 vs 9.0+/-2.4 h). The cell number of blastocysts 70 h after treatment and developmental ability of blastocysts after transfer to pseudopregnant recipients were the same for the reduced and control groups. The present study indicates that the nucleo/cytoplasmic ratio of embryos may possibly be an important factor that determines the time of blastocele formation. 相似文献
28.
Summary A 1.2-kb DNA fragment of the cytochrome oxidase subunit I (CO I) gene of mitochondria isolated from an ascidian,Halocynthia roretzi, was amplified by polymerase chain reaction (PCR) and sequenced. Codons AGA and AGG appeared in its reading frame, indicating
that these are sense codons in this organelle. Sequence comparisons with the corresponding regions of other animal mitochondrial
CO I genes suggest that codons AGA and AGG correspond to glycine in the ascidian mitochondrial genome, but not to serine as
in most invertebrate genomes, nor to stops as in vertebrate genomes. The other codons are identical to those of vertebrate
mitochondria. 相似文献
29.
Norio Tada Takuya Sakamoto Akihiko Kagami Keiko Mochizuki Kosei Kurosaka 《Molecular and cellular biochemistry》1993,119(1-2):171-178
Human plasmain vitro inhibits the growth of coagulase negative staphylococci,S. epidermidis, which may be pathogenic in the immunocompromised host. To determine the antimicrobial components, serum was fractionated by column chromatography, which revealed that elution areas where lipoproteins can be yielded had high antimicrobial activity againstS. epidermidis. Therefore, lipoprotein fractions, including very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL), were separated by ultracentrifugation and incubated withS. epidermidis. All 3 lipoprotein fractions suppressed bacterial growth within the first 3 h but VLDL enhanced bacterial growth after 9 h of incubation compared with the control. HDL, however, inhibited bacterial growth throughout 21 h of incubation.To confirm these results, serum from healthy volunteers was separated by ion exchange column chromatography and again by HPLC to purify the antimicrobial fraction. In the protein analysis with gradient polyacrylamide-SDS gel, apolipoprotein Al (apo Al), which is a major apolipoprotein of HDL, was detected in the antimicrobial fraction. Therefore, this fraction was loaded onto an immunoaffinity column coupled with the anti-apo Al monoclonal antibody (Mab). Unbound fraction had no antimicrobial activity, but anti-S. epidermidis activity was recovered from the bound fraction which consisted mainly of apo Al, All and apo C in protein composition.These results indicated that the antimicrobial activity was associated with the apo Al-containing lipoprotein particles (HDL). This property of HDL may directly affect bacterial growth and promote the self-defense mechanisms of normal and immunocompromised individuals. 相似文献