全文获取类型
收费全文 | 2058篇 |
免费 | 128篇 |
国内免费 | 33篇 |
专业分类
耳鼻咽喉 | 16篇 |
儿科学 | 65篇 |
妇产科学 | 46篇 |
基础医学 | 291篇 |
口腔科学 | 32篇 |
临床医学 | 131篇 |
内科学 | 449篇 |
皮肤病学 | 83篇 |
神经病学 | 97篇 |
特种医学 | 86篇 |
外科学 | 253篇 |
综合类 | 162篇 |
预防医学 | 102篇 |
眼科学 | 52篇 |
药学 | 156篇 |
中国医学 | 6篇 |
肿瘤学 | 192篇 |
出版年
2023年 | 8篇 |
2022年 | 22篇 |
2021年 | 43篇 |
2020年 | 30篇 |
2019年 | 40篇 |
2018年 | 40篇 |
2017年 | 19篇 |
2016年 | 26篇 |
2015年 | 48篇 |
2014年 | 74篇 |
2013年 | 79篇 |
2012年 | 97篇 |
2011年 | 113篇 |
2010年 | 85篇 |
2009年 | 70篇 |
2008年 | 88篇 |
2007年 | 102篇 |
2006年 | 108篇 |
2005年 | 100篇 |
2004年 | 81篇 |
2003年 | 70篇 |
2002年 | 57篇 |
2001年 | 62篇 |
2000年 | 51篇 |
1999年 | 44篇 |
1998年 | 43篇 |
1997年 | 49篇 |
1996年 | 39篇 |
1995年 | 25篇 |
1994年 | 24篇 |
1993年 | 27篇 |
1992年 | 29篇 |
1991年 | 31篇 |
1990年 | 27篇 |
1989年 | 32篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 23篇 |
1985年 | 37篇 |
1984年 | 17篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1979年 | 15篇 |
1978年 | 18篇 |
1977年 | 11篇 |
1976年 | 18篇 |
1975年 | 28篇 |
1974年 | 18篇 |
1973年 | 12篇 |
排序方式: 共有2219条查询结果,搜索用时 15 毫秒
11.
Choleraphage φ149 DNA is a linear double-stranded molecule 69 × 106 Da or 104 kilobase pairs (kbp). From restriction enzyme analysis, it has been concluded that the DNA is circularly permuted. There are at least three S1 nuclease-sensitive sites along the length of the molecule. These sites represent single-strand interruptions repairable by T4 DNA ligase. A physical map of the DNA has been constructed using the restriction endonucleases BamH1 and BglII. 相似文献
12.
13.
Development of hatching blastocysts from immature human oocytes following in-vitro maturation and fertilization using a co-culture system 总被引:8,自引:0,他引:8
Hwu YM; Lee RK; Chen CP; Su JT; Chen YW; Lin SP 《Human reproduction (Oxford, England)》1998,13(7):1916-1921
Recently, in-vitro maturation (IVM) of immature human oocytes recovered
from non-stimulated follicles has been applied in the treatment of
infertility. However, in previous reports, very few embryos cultured in
conventional medium have reached the expanded blastocyst stage following
in-vitro maturation and fertilization (IVM/IVF). The objective of this
study was to investigate whether the developmental competence of human
embryos following IVM/IVF could be enhanced by the use of a human ampullary
cell co-culture system. Immature human oocytes were aspirated from small
follicles at Caesarean section and then cultured in medium containing human
menopausal gonadotrophin for 36 to 48 h, followed by insemination. Zygotes
were randomly cultured either in conventional culture medium alone or in
the co-culture system. Of 48 embryos cultured in conventional medium alone,
all arrested at the 2-16- cell stage on day 3 after insemination. Of 46
embryos cultured in the co-culture system, 26 embryos (56.5%) arrested at
the 2-16-cell stage. Six embryos (13%) developed to the morula stage.
Fourteen embryos (30.4%) developed to expanded blastocysts and two
blastocysts were hatching on day 7 after insemination. We conclude that
co-culture significantly enhances the development of blastocysts in embryos
resulting from IVM/IVF.
相似文献
14.
15.
16.
Detection of chromosomes and estimation of aneuploidy in human spermatozoa using fluorescence in-situ hybridization 总被引:11,自引:0,他引:11
The development and application of fluorescence in-situ hybridization
(FISH) has opened the way for comprehensive studies on numerical chromosome
abnormalities in human spermatozoa. FISH can be rapidly applied to large
numbers of spermatozoa and thus overcomes the major limitation of
karyotyping spermatozoa after penetration of zona-free hamster oocytes. The
simultaneous hybridization of two or more chromosome-specific probes to
spermatozoa and subsequent detection of the bound probes using different
fluorescent detection systems enables two or more chromosomes to be
localized simultaneously in the same spermatozoon and provides a technique
for undertaking reasonable estimates of aneuploidy. The most commonly used
probes are those which bind to the centromeric region of specific
chromosomes. Most studies to date have concentrated on estimating
aneuploidy in spermatozoa from normospermic men, although reports are
beginning to appear on aneuploidy in spermatozoa from subfertile and
infertile men. Multi- probe FISH studies have generally reported disomy
(hyperhaploidy) estimates of 0.05-0.2% per chromosome. There is preliminary
evidence that some chromosomes such as X, Y and 21 are predisposed towards
higher rates of non-disjunction during spermatogenesis. There are also
suggestions of inter-donor variability in aneuploidy frequencies for
specific chromosomes, although this requires confirmation in larger
studies. While FISH is clearly a powerful technique that has many
applications in reproductive medicine, it must also be realized that it
does have limitations and the technology itself is still evolving and has
yet to be fully validated on spermatozoa.
相似文献
17.
A silencing pathway to induce H3-K9 and H4-K20 trimethylation at constitutive heterochromatin 总被引:31,自引:1,他引:31 下载免费PDF全文
Schotta G Lachner M Sarma K Ebert A Sengupta R Reuter G Reinberg D Jenuwein T 《Genes & development》2004,18(11):1251-1262
Histone lysine methylation is a central modification to mark functionally distinct chromatin regions. In particular, H3-K9 trimethylation has emerged as a hallmark of pericentric heterochromatin in mammals. Here we show that H4-K20 trimethylation is also focally enriched at pericentric heterochromatin. Intriguingly, H3-K9 trimethylation by the Suv39h HMTases is required for the induction of H4-K20 trimethylation, although the H4 Lys 20 position is not an intrinsic substrate for these enzymes. By using a candidate approach, we identified Suv4-20h1 and Suv4-20h2 as two novel SET domain HMTases that localize to pericentric heterochromatin and specifically act as nucleosomal H4-K20 trimethylating enzymes. Interaction of the Suv4-20h enzymes with HP1 isoforms suggests a sequential mechanism to establish H3-K9 and H4-K20 trimethylation at pericentric heterochromatin. Heterochromatic H4-K20 trimethylation is evolutionarily conserved, and in Drosophila, the Suv4-20 homolog is a novel PEV modifier to regulate position-effect variegation. Together, our data indicate a function for H4-K20 trimethylation in gene silencing and further suggest H3-K9 and H4-K20 trimethylation as important components of a repressive pathway that can index pericentric heterochromatin. 相似文献
18.
Preimplantation embryo morphology following early luteal phase anti-nidatory treatment with mifepristone (RU486) in the rhesus monkey 总被引:6,自引:0,他引:6
Ghosh D Lalitkumar PG Wong VJ Hendrickx AG Sengupta J 《Human reproduction (Oxford, England)》2000,15(1):180-188
The ultrastructural characteristics of peri-implantation stage embryos recovered on day 6 after ovulation from rhesus monkeys with or without mifepristone (RU486) treatment during the early luteal phase were examined in the present study. Monkeys were randomly allocated to two groups; group 1 animals were injected s.c. with 2 ml vehicle (1:4, benzyl benzoate: olive oil, v/v, n = 21) and group 2 animals received a single dose of mifepristone (2 mg/kg body weight, w/v, n = 30) in the same volume of vehicle on day 2 after ovulation in mated cycles. On day 6 after ovulation, female monkeys of both groups were laparotomized and their reproductive tracts were flushed to retrieve preimplantation stage embryos. Embryos that showed frank degeneration or desynchrony on gross microscopical examination were not included in the present study. Preimplantation embryo growth on day 6 after ovulation was significantly (P < 0.05) affected in the morula-blastocyst transition stage in mifepristone-treated monkeys compared with that in the control group of monkeys. Ultrastructurally, administration of mifepristone on day 2 after ovulation depressed preimplantation stage embryo development, characterized by loss of cell polarity, lack of mitochondrial maturity, and lack of differentiation in trophoblast cells. Furthermore, preimplantation embryos from mifepristone-treated animals displayed a higher occurrence of inter-blastomere space, intra-cytoplasmic vacuoles, myelinoid bodies, accumulation of lipid droplets, lysosomes, lipofuscins, autophagosomes and multivesicular bodies. Collectively, it appears that the developmental potential of preimplantation embryos was significantly compromised in mifepristone-treated cycles. 相似文献
19.