全文获取类型
收费全文 | 4227篇 |
免费 | 581篇 |
国内免费 | 3篇 |
出版年
2022年 | 47篇 |
2021年 | 76篇 |
2019年 | 47篇 |
2018年 | 68篇 |
2017年 | 60篇 |
2016年 | 81篇 |
2015年 | 142篇 |
2014年 | 189篇 |
2013年 | 211篇 |
2012年 | 285篇 |
2011年 | 248篇 |
2010年 | 166篇 |
2009年 | 137篇 |
2008年 | 203篇 |
2007年 | 182篇 |
2006年 | 148篇 |
2005年 | 161篇 |
2004年 | 144篇 |
2003年 | 136篇 |
2002年 | 131篇 |
2001年 | 84篇 |
2000年 | 69篇 |
1999年 | 71篇 |
1998年 | 51篇 |
1997年 | 36篇 |
1996年 | 42篇 |
1992年 | 57篇 |
1991年 | 82篇 |
1990年 | 59篇 |
1989年 | 74篇 |
1988年 | 54篇 |
1987年 | 58篇 |
1986年 | 55篇 |
1985年 | 57篇 |
1984年 | 70篇 |
1983年 | 44篇 |
1982年 | 46篇 |
1981年 | 37篇 |
1980年 | 39篇 |
1979年 | 61篇 |
1978年 | 41篇 |
1977年 | 58篇 |
1976年 | 33篇 |
1975年 | 45篇 |
1974年 | 46篇 |
1973年 | 51篇 |
1972年 | 49篇 |
1971年 | 34篇 |
1970年 | 39篇 |
1969年 | 41篇 |
排序方式: 共有4811条查询结果,搜索用时 890 毫秒
191.
An ocellus of the horseshoe crab, Limulus polyphemus, has been serially sectioned for light and electron microscopy, its sensory cells have been indexed, and the interconnections of a third of these traced. The ocellus contains 155 retinula cells and 26 arhabdomeric cells, which are secondary sensory neurons. Of these, 55 retinula cells constitute 7 quasi-ommatidial assemblages, each innervated by at least one and a total of 9 arhabdomeric cells. When known electrotonic coupling patterns are compared with gap-junctional connections, retinula cells sensitive to visible or ultraviolet light can be tentatively identified. Retinula cell axons contribute collaterals to a synaptic plexus, in which the arhabdomeric cells apparently do not participate. 相似文献
192.
The influence of posture and age on urinary protein excretion was studied in 120 normal men volunteers. The supine excretion rate was less than 140 mug/min in all but two people (median value 38 mug/min) and tended to increase with age. The excretion rate decreased on quiet standing in 80% of people, which corresponded to a fall in creatinine-clearance. In the remaining 20% protein excretion increased on standing but generally remained within normal limits and was dissociated from changes in creatinine clearances. This increase was more prevalent in younger people and may represent a phenomenon analogous to orthostatic proteinuria, differing only quantitatively. 相似文献
193.
Dwight R. Robinson Howard Smith Mary B. McGuire Lawrence Levine 《Prostaglandins & other lipid mediators》1975,10(1):67-85
The synthesis of prostaglandins by rheumatoid synovial tissue in organ culture was studied utilizing radioimmunoassay, with antisera to PGB1, PGF1α and PGF2α. It was established that PGE2 and PGF2α were the major prostaglandins formed by analyses of culture media with the two antisera to PGF, before and after alkali treatment. Indomethacin at 5 μg/ml suppressed prostaglandin synthesis, usually to <1% of control cultures. Colchicine, 0.1 μg/ml resulted in marked stimulation of prostaglandin synthesis, in some cases over 10 fold. It is suggested, because of the colchicine effect, that the state of the microtubules may regulate the rate of prostaglandin biosynthesis. It is possible that prostaglandin E2 produced by rheumatoid synovia may contribute to the pathogenesis of the inflammatory reaction and lead to destruction of juxta-articular bone in rheumatoid arthritis. 相似文献
194.
195.
Stéphanie Rollero Audrey Bloem Anne Ortiz-Julien Florian F. Bauer Carole Camarasa Benoit Divol 《Environmental microbiology》2019,21(11):4076-4091
In grape must, nitrogen is available as a complex mixture of various compounds (ammonium and amino acids). Wine yeasts assimilate these multiple sources in order to suitably fulfil their anabolic requirements during alcoholic fermentation. Nevertheless, the order of uptake and the intracellular fate of these sources are likely to differ between strains and species. Using a two-pronged strategy of isotopic filiation and RNA sequencing, the metabolic network of nitrogen utilization and its regulation in Kluyveromyces marxianus were described, in comparison with those of Saccharomyces cerevisiae. The data highlighted differences in the assimilation of ammonium and arginine between the two species. The data also revealed that the metabolic fate of certain nitrogen sources differed, thereby resulting in the production of various amounts of key wine aroma compounds. These observations were corroborated by the gene expression analysis. 相似文献
196.
During infection a λ phage that is incapable of DNA replication requires recombination for maturation. If two prophages are situated in tandem, this requirement for DNA replication and recombination is bypassed. In physical experiments using the DNA cutting assay of Freifelder et al. (1973), the DNA of a sex factor containing one or two prophages defective in both excision and DNA replication is cut efficiently only when two prophages are in tandem. We interpret this to mean that λ can only be matured from a structure of greater than unit length, and hypothesize that the structure must contain two joined ends (AR-joints). 相似文献
197.
Genetically modified cells of Pseudomonas fluorescens, chromosomally marked with genes for bioluminescence, were inoculated into sterile soil microcosms. During incubation for 90 days, viable cell concentration did not change significantly but light output, measured by luminometry, decreased, indicating reduced metabolic activity due to lack of substrates. Amendment with nutrients resulted in parallel increases in both luminescence and dehydrogenase activity. Luminometry therefore enables rapid monitoring of the activity of populations of luminescence-marked microbial inocula in the soil, with greater sensitivity and selectivity than traditional techniques. 相似文献
198.
199.
200.