全文获取类型
收费全文 | 4575篇 |
免费 | 252篇 |
国内免费 | 1篇 |
出版年
2022年 | 21篇 |
2021年 | 53篇 |
2020年 | 30篇 |
2019年 | 41篇 |
2018年 | 56篇 |
2017年 | 55篇 |
2016年 | 89篇 |
2015年 | 121篇 |
2014年 | 135篇 |
2013年 | 269篇 |
2012年 | 252篇 |
2011年 | 268篇 |
2010年 | 157篇 |
2009年 | 140篇 |
2008年 | 281篇 |
2007年 | 244篇 |
2006年 | 237篇 |
2005年 | 273篇 |
2004年 | 233篇 |
2003年 | 232篇 |
2002年 | 237篇 |
2001年 | 123篇 |
2000年 | 129篇 |
1999年 | 102篇 |
1998年 | 67篇 |
1997年 | 75篇 |
1996年 | 43篇 |
1995年 | 28篇 |
1994年 | 42篇 |
1993年 | 26篇 |
1992年 | 76篇 |
1991年 | 69篇 |
1990年 | 64篇 |
1989年 | 57篇 |
1988年 | 81篇 |
1987年 | 51篇 |
1986年 | 35篇 |
1985年 | 29篇 |
1984年 | 37篇 |
1983年 | 26篇 |
1982年 | 26篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 24篇 |
1978年 | 26篇 |
1975年 | 18篇 |
1974年 | 13篇 |
1973年 | 21篇 |
1971年 | 12篇 |
1968年 | 12篇 |
排序方式: 共有4828条查询结果,搜索用时 15 毫秒
971.
Koji Takechi Hideyuki Tamura Kiyoshi Yamaoka Hiromu Sakurat 《Free radical research》1997,26(6):483-496
In pharmacokinetic studies, a variety of analytical method including radioisotopic detection and HPLC (high performance liquid chromatography) has been used. In the present investigation, we developed in vivo BCM (Blood Circulation Monitoring)-ESR method, which is a new technique with a conventional X-band ESR spectrometer for observing stable free radicals in the circulating blood of living rats under anaesthesia. Both 5-(PROXYL derivatives) and 6-(TEMPO derivatives) membered nitroxide spin probes with various types of substituent functional group were used. After physicochemical properties of the spin probes such as hyperfine coupling constant (A-value), g-value and partition coefficient as well as chemical stability of the compounds in the fresh blood were obtained, the in vivo BCM-ESR method was performed in normal rats. Several pharmacokinetic parameters such as half-life of the probes, distribution volume, total body clearance and mean residence time were obtained and discussed in terms of their chemical structures. In addition, clearance of a spin probe was related to the urine concentration. The BCM-ESR method was found to be very useful to observe free radicals at the real time. By time-dependent ESR signal decay of spin probes, pharmacokinetic parameters were obtained. 相似文献
972.
Suzuki Y Haruna Y Kobayashi H Kawakubo K Goto S Gunji A 《Journal of gravitational physiology : a journal of the International Society for Gravitational Physiology》1997,4(2):P123-P124
Due to prolonged bed rest (BR), maximal oxygen uptake (VO2max) might be decreased by above -8%, even if a moderate supine bicycle exercise (SBE) was performed for 45 to 60 minutes every day during BR. However, the decrement of VO2max was lowered to below -5% by isometric training and using a reverse gradient garment. Further it was rather slightly increased by SBE training with gradually increasing load from 40% to 90% VO2max. The facts suggest the dependency of the decrease of VO2max during BR on exercising muscle mass (MM) and strength. In the present study, therefore, the effects of isokinetic knee extension (Ik-KnE) training on VO2max, exercising MM and muscle contraction strength during BR were investigated. Then, the relationships between changes in VO2max and the muscle mass and strength were considered. 相似文献
973.
RGM1, a cell line derived from normal gastric mucosa of rat 总被引:10,自引:0,他引:10
974.
Suzuki Y Akima H Igawa S Fukunaga T Kawakub K Goto S Makita Y Gunji A 《Journal of gravitational physiology : a journal of the International Society for Gravitational Physiology》1996,3(2):42-43
Ten individuals underwent 20 days of horizontal bed rest for this study of the influence of muscle mass and strength on bone mineral density. Muscle mass volume and cross sectional area were measured using magnetic resonance imaging and bone mineral density was determined by dual energy X-ray absorptiometry before and after bed rest. Measurements were made at various parts of the leg, including the knee. Gender differences were also determined. Results are presented and discussed. 相似文献
975.
Ken-ichi Hisamatsu Tetsuya Ganbo Tsutomu Nakazawa Mayumi Nakajima Rei Goto Yosihiko Murakami 《Prostaglandins & other lipid mediators》1996,51(1):69-79
To clarify the effects of leukotriene C4 (LTC4) on human ciliated epithelium, ciliary activity of the ethmoid sinus mucosa was measured photoelectrically in tissue culture. At concentrations ranging from 10−6M to 10−9M, LTC4 showed minimal effects on the ciliated epithelium during the initial 30 minutes of exposure; thereafter, ciliary inhibition was observed in a concentration- and time-dependent manner. Irrigation of the mucosa with culture medium 15 minutes after exposure prevented the LTC4-induced ciliary inhibition. However, irrigation 60 minutes after exposure failed to inhibit 10−8M LTC4-induced ciliary dysfunction and mucosal damage. The LTC4-induced ciliary inhibition was blocked in the presence of FPL-55712 and/or Ly-171883, both leukotriene receptor antagonists. L-serine and sodium tetraborate complex (SBC), a γ-glutamyl transpeptidase (γ-GTP) inhibitor, also inhibited the LTC4-induced ciliary inhibition. These findings indicate that LTC4 is converted to LTD4 by γ-GTP during 60 minutes of exposure, and LTC4 itself has minimal direct effects on the ciliated cells. 相似文献
976.
Genetic differentiation of the two sibling species,Cottus nozawae andC. amblystomopsis, from the northern part of Japan (Hokkaido Island and the Tohoku District) was investigated using allozyme variations and
restriction fragment length polymorphisms of mitochondrial DNA. Although the two species are morphologically very similar,
previously being thought to be a single species, they have different life-cycles;C. nozawae has a fluvial life-cycle with a small number of large-sized eggs, whereasC. amblystomopsis is an amphidromous species with a large number of small-sized eggs. Four populations ofC. amblystomopsis from Hokkaido Island and 24 populations ofC. nozawae (22 from Hokkaido Island and 2 from the Tohoku District) were sampled and examined Intrapopulational differentiation in the
two species was measured by examining several indexes, including proportion of polymorphic loci (P), mean heterozygosity (H)
and nucleotide diversity (π). All measurements were higher in theC. amblystomopsis populations, suggesting that intrapopulational variation inC. nozawae was less than inC. amblystomopsis and reflecting the difference in effective population sizes between them. Cluster analyses were performed using the UPGMA
method, based on the data matrices of genetic distance (D) and the net nucleotide difference (δ) between populations. TheC. nozawae andC. amblystomopsis populations from Hokkaido Island composed a large cluster (Hokkaido group), while theC. nozawae populations from the Tohoku District composed a different cluster (Tohoku group). Bootstrap probabilities deduced from 1000
bootstrap replications for presence or absence of restriction sites showed that the mtDNA haplotypes detected within the Tohoku
Group occurred in 99.9% of the bootstrap replicates outside the mtDNA haplotypes of the Hokkaido group, while those within
the Hokkaido group occurred in 3.5–64.9% of bootstrap replicates. Consequently, the Hokkaido populations of the two species
(Hokkaido group) were genetically close to each other, whileC. nozawae from the Tohoku District (Tohoku group) were distant from the Hokkaido group. These results suggest that the ancestral populations
of the two species on Hokkaido Island shared the same gene pool, even after becoming geographically isolated from the ancestral
population ofC. nozawae in the Tohoku District by the formation of the Tsugaru Straits. 相似文献
977.
Zhu XuFen Suzuki Kengo Saito Takeshi Okada Kazunori Tanaka Katsunori Nakagawa Tsuyoshi Matsuda Hideyuki Kawamukai Makoto 《Plant molecular biology》1997,35(3):331-341
We have cloned a new geranylgeranyl pyrophosphate (GGPP) synthase gene, designated GGPS6/, from Arabidopsis thaliana genomic DNA. Nucleotide sequence analysis revealed that the GGPS6 gene contains an open reading frame coding for a protein of 343 amino acid residues with a calculated molecular mass of 37 507 Da. Also, the gene is not interrupted by an intron. The predicted amino acid sequence of the GGPS6 gene shows significant homology (34.0–57.7%) with other GGPP synthases from Arabidopsis. The GGPS6 protein contains a N-terminal signal peptide which is thought to function as an organelle targeting sequence. In fact, the GGPS6-GFP fusion protein was found to be localized exclusively in mitochondria when expressed in tobacco BY-2 cells. In vitro analysis of the enzyme activity as well as genetic complementation analysis with Erwinia uredovora crt gene cluster expressed in Escherichia coli showed that the GGPS6 gene most certainly encodes a GGPP synthase catalyzing the conversion of farnesyl pyrophosphate to GGPP. 相似文献
978.
The effect of regucalcin, a Ca2+-binding protein, on Ca2+ transport system in rat renal cortex microsomes was investigated. The presence of regucalcin (10-8 to 10-6 M) in the reaction mixture caused a significant increase in Ca2+-ATPase activity and ATP-dependent45 Ca2+ uptake in the microsomes. Regucalcin (10-7 M) increased Ca2+-ATPase activity independently of increasing concentrations of CaCl_2. The microsomal Ca2+-ATPase activity and45 Ca2+ uptake were markedly decreased by the presence of vanadate (0.1 mM) or N-ethylmaleimide (NEM; 5 mM) in the absence or presence of regucalcin. Dithiothreitol (DTT; 5 mM) markedly elevated Ca2+-ATPase activity and 45Ca2+ uptake in the microsomes. The DTT effects were not further enhanced by regucalcin (10-7 M). Meanwhile, the microsomal Ca2+-ATPase activity and 45Ca2+ uptake were significantly decreased by the presence of dibutyryl cyclic AMP (DcAMP; 10-5 and 10-3 M) or inositol 1,4, 5-trisphosphate (IP3; 10-7 and 10-5 M). The effect of regucalcin (10-7 M) on Ca2+ ATPase activity and 45Ca2+ uptake was weakened in the presence of DcAMP or IP3. The present results demonstrate that regucalcin has a stimulatory effect on ATP-dependent Ca2+ uptake in the microsomes of rat renal cortex due to acting on the thiol groups of Ca2+-ATPase. 相似文献
979.
Genetic evidence supporting the existence of two distinct species in the genusGasterosteus around Japan 总被引:1,自引:0,他引:1
Synopsis The genetic and morphological features ofGasterosteus aculeatus were investigated for 29 populations around Japan. Allozyme analyses recognized two groups (Pacific Ocean group and Japan Sea group) that had distinct characteristic features, and showed high genetic differentiation between them (D = 0.482). The Pacific Ocean group had a wide range, from North America to Japan, along the Pacific coast. The distribution of the Japan Sea group was limited around the Sea of Japan and the Sea of Okhotsk. The distribution of these groups were found to be sympatric on the Pacific coast of Hokkaido Island, Japan. From this area, genetic analyses demonstrated that the sympatric populations of the two groups formed independent breeding stocks, and it is considered that the two groups were reproductively isolated from each other. Additionally, each group had distinctive morphological features of lateral plates and caudal keels in the sympatric area. These results suggested that these two groups of the threespine stickleback comprise different species and that the Japan Sea group is taxonomically distinguishable fromG. aculeatus. 相似文献
980.
Using an isogenic line of rice having lazy gene (la), we studied the correlation between the agravitropic response at the young seedling stage and the lazy habit (prostrate
growth of tillers) at the more advanced stage of growth. In this study, it was found that both agravitropism and lazy habit
were controlled by the single recessivela gene. That is, F2 segregants of Kamenoo×lazy-Kamenoo, which had an agravitropic response at their young seedling stage, showed a lazy habit
of growth in the more advanced stage of vegetative growth. On the other hand, seedlings that showed normal gravitropic curvature
at their early stage of growth had an upright growth in the mature stage. 相似文献