首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1911篇
  免费   91篇
  2002篇
  2023年   15篇
  2022年   22篇
  2021年   50篇
  2020年   29篇
  2019年   30篇
  2018年   59篇
  2017年   63篇
  2016年   68篇
  2015年   81篇
  2014年   88篇
  2013年   157篇
  2012年   123篇
  2011年   156篇
  2010年   104篇
  2009年   63篇
  2008年   86篇
  2007年   93篇
  2006年   82篇
  2005年   57篇
  2004年   59篇
  2003年   63篇
  2002年   58篇
  2001年   18篇
  2000年   10篇
  1999年   4篇
  1998年   15篇
  1997年   11篇
  1996年   6篇
  1995年   3篇
  1994年   2篇
  1993年   3篇
  1992年   3篇
  1991年   7篇
  1985年   4篇
  1984年   4篇
  1983年   3篇
  1982年   4篇
  1981年   5篇
  1978年   5篇
  1977年   3篇
  1971年   2篇
  1955年   29篇
  1954年   77篇
  1953年   42篇
  1952年   27篇
  1951年   20篇
  1950年   56篇
  1949年   12篇
  1948年   5篇
  1947年   3篇
排序方式: 共有2002条查询结果,搜索用时 15 毫秒
91.
The aim of the study was the analysis of frequency of yeast-like fungi as etiological agents of fungemias in patients hospitalized in operative and conservative wards of Medical Academy Central Clinical Hospital in Warsaw in 1998-1999. Peripheral blood samples and collected from vascular catheters were incubated in BacT/Alert system(Organon Teknika, USA). Positive blood samples were inoculated on Sabouraud medium with chloramphenicol (bioMerieux, France) (the time of cultivation from 48 h to 7 days at 30 C) and on chromogenic medium BBL CHROMagar Candida (Becton Dickinson, USA). Fungal strains were identified by standard mycological procedures using ID 32 C strips (ATB system, bioMerieux, France) and tests of Sanofi Diagnostics Pasteur (France). The total number of positive blood cultures was 1724. Fifty eight fungal strains were isolated from blood samples (3.36%). Strains belonged to 4 genera: Candida (55), Trichosporon (1), Saccharomyces (1) and Pichia (1). Thirty eight fungal strains were isolated from peripheral blood samples. Forty seven fungal strains were cultured from patients hospitalized in operative wards. Among fungi isolated from peripheral blood samples C. albicans (10), C. glabrata (9) and C. parapsilosis (5) strains dominated. From blood samples collected from vascular catheters most often C. albicans (7), C. glabrata (4) and C. parapsilosis (3) were isolated.  相似文献   
92.
The C-banding patterns of twelve weevil species are presented. The obtained results confirm the existence of two groups of species: with a small or large amount of heterochromatin in the karyotype. The first group comprises seven species (Apionidae: Holotrichapion pisi; Curculionidae: Phyllobius urticae, Ph. pyri, Ph. maculicornis, Tanymecus palliatus, Larinodontes turbinatus, Cionus tuberculosus). In weevils with a small amount of heterochromatin, tiny grains on the nucleus in interphase are visible, afterwards in mitotic and meiotic prophase appearing as dark dots. The absence of C-bands does not indicate a lack of heterochromatin but heterochromatic regions are sometimes so small that the condensation is not visible during the cell cycle. The second group comprises five species (Otiorhynchus niger, O. morio, Polydrusus corruscus, Barypeithes chevrolati, Nedyus quadrimaculatus) which possess much larger heteropicnotic parts of chromosomes visible during all nuclear divisions. The species examined have paracentromeric C-bands on autosomes and the sex chromosome X, except for Otiorhynchus niger, which also has an intercalary bands on one pair of autososomes. All the species examined differ in the size of segments of constitutive heterochromatin. The y heterochromosome is dot-like and wholly euchromatic in all the studied species.  相似文献   
93.
Food consumption was measured during the day (lights on) and the night (lights off) and compared between one outbred and 9 inbred strains of mice (CBA/Kw, C3H, DBA2, KP, BALB/c, C57BL, B10.Amst, B10.BR, B10.BR Y-del) in age groups 30-60, 60-90, 90-120, and more than 120 days. Outbred mice and animals from B10 sublines ate significantly more during nocturnal darkness. Day and night food consumption was similar in KP animals. In mice from the remaining strains there was an apparent age-related shift from nocturnal towards diurnal eating habits.  相似文献   
94.
A salient feature of shoot meristem growth is the maintenance of distinct anatomical and morphological features despite a continuous flux of cells. To investigate how meristem organization is self-perpetuated, we developed a protocol for the analysis of meristem growth in 3-D. Our protocol uses a non-destructive replica method to follow the pattern of cell expansion and cell divisions on the meristem surface over several days. Algorithms to reconstruct the meristem surface and compute its curvature and rate of extension were implemented. We applied this approach to the shoot apical meristem of Anagallis arvensis and showed that a subcellular resolution of extension rates can be achieved. This is the first detailed quantitative analysis of meristem geometry and surface expansion in 3-D. This new approach will be useful to connect cellular activities such as cell expansion, cell division, and differential gene expression with overall meristem morphogenesis.  相似文献   
95.
Folliculogenesis was studied daily in the 18 oestrous cycles in six prolific Olkuska ewes from October to December using transrectal ultrasonography to record the number and size of all ovarian follicles > or =2 mm in diameter. Blood samples were taken once a day and were analyzed for concentrations of FSH, LH, estradiol and progesterone. Follicular and hormonal data were analyzed for associations between different stages of development of the follicular waves and concentrations of FSH and estradiol. The first wave during which at least one follicle reached maximum diameter of > or =4 mm after ovulation, was defined as a wave 1, and the following waves were numbered sequentially. Waves 1, 2, 3, 4 and the ovulatory one emerged on days: -2 to 4, 4 to 8, 6 to 11, 10 to 12 and 11 to 15, respectively. The mean number of follicles per wave that reached diameter of > or =4 mm was 4.15 +/- 1.1 and 16.62 +/- 8.6 follicles per estrous cycle of a total 299 follicles were observed. Significantly more follicles (p> or =0.05) emerged on days 2, 8 and 13 than in other days. Serum FSH concentrations fluctuated from 0.11 ngml(-1) on day 2 to preovulatory maximum 1.81 ngml(-1) on day 17 of the estrous cycle. The emergence of follicular waves was associated with elevations of FSH concentrations in blood serum. The mean increase in FSH concentration was followed by the recruitment of follicles of the next wave. The mean daily FSH concentration and the mean number of follicles emerging each day were negatively correlated. The length of the interwave interval (4.4 +/- 1.6 days) did not differ significantly from the interval between pulses of FSH (4.8 +/- 0.3 days). The mean serum estradiol concentrations showed fluctuations until day 14 and then gradually increased from 5.47 +/- 0.3 pgml(-1) to reach a peak 13.14 +/- 0.2 pgml(-1) on the day before ovulation. To summarize, the growth of ovarian follicles during the estrous cycle in high fecundity Olkuska sheep exhibited a distinct wave-like pattern. Ovarian follicles emerged from the pool of 2 mm follicles. The preovulatory follicles originated from the large follicle population were present in the ovary at the time of luteal regression. The initial stages of the growth of the largest follicles appears to be controlled primarily by increases in FSH secretion.  相似文献   
96.
The present study describes an analysis of genotype and allele distribution at the porcine GH locus among day-10 pig embryos. Embryos were collected post mortem from 6 crossbred (Danish Landrace x Yorkshire) sows inseminated with mixed Duroc semen and individually frozen for later analysis. After extraction, DNA was subjected to PCR amplification and restriction analysis with Msp I and Hae II enzymes. The genotype frequencies were: Msp I CD 0.17, DD 0.83; and Hae II AA 0.33, AB 0.58; and BB 0.09. The Msp I CC genotype was not found among analysed embryos. To our knowledge, this is the first report on the genotype and allele distribution at the GH locus among early pig embryos.  相似文献   
97.
98.
The influence of BA, GA3 and IAA applied successively onflower bud formation in shoot apices of Pharbitis nil hasbeen investigated. The shoot apices were isolated from seedlings cultivatedunder non-inductive continuous light and from seedlings exposed to asubinductive (12 h) dark period. BA and GA3 introducedsuccessively into culture medium replaced the inductive night, causing theflowering of plantlets in completely non-inductive continuous light (optimalconcentration of BA – 10–7–10–6mol dm–3, GA3 –10–7–10–6 moldm–3) and stimulated this process under thesubthresholdinduction. These hormones applied in reverse sequence (in the first placeGA3, then BA) did not affect flowering of explants. IAA nullifiedthestimulating effect of BA and GA3. The influence of phytohormones onflowering may result from the change of growth correlations within the shootapical meristem.  相似文献   
99.
Fifteen (soil and intestinal) strains of Desulfovibrio desulfuricans species were typed by PCR method with the use of primers specific for repetitive extragenic palindromic (REP) and enterobacterial repetitive intergenic consensus (ERIC) sequences. As a result, characteristic DNA fingerprints for the strains were obtained. Moreover, the genetic profiles were found to be useful for typing and distinguishing the strains of D. desulfuricans. According to cluster analysis, PCR with primers complementary to the sequences REP appeared to be slightly more discriminatory than PCR with ERIC primers for the investigated strains. Distinct fingerprint patterns of two isolates derived from the same patient pointed to the different origin of both strains.  相似文献   
100.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号