全文获取类型
收费全文 | 5569篇 |
免费 | 363篇 |
出版年
2021年 | 59篇 |
2020年 | 26篇 |
2019年 | 43篇 |
2018年 | 64篇 |
2017年 | 55篇 |
2016年 | 86篇 |
2015年 | 123篇 |
2014年 | 174篇 |
2013年 | 310篇 |
2012年 | 254篇 |
2011年 | 276篇 |
2010年 | 169篇 |
2009年 | 164篇 |
2008年 | 245篇 |
2007年 | 296篇 |
2006年 | 262篇 |
2005年 | 244篇 |
2004年 | 278篇 |
2003年 | 274篇 |
2002年 | 279篇 |
2001年 | 194篇 |
2000年 | 215篇 |
1999年 | 171篇 |
1998年 | 94篇 |
1997年 | 83篇 |
1996年 | 62篇 |
1995年 | 55篇 |
1994年 | 46篇 |
1993年 | 45篇 |
1992年 | 92篇 |
1991年 | 115篇 |
1990年 | 102篇 |
1989年 | 98篇 |
1988年 | 82篇 |
1987年 | 85篇 |
1986年 | 79篇 |
1985年 | 82篇 |
1984年 | 63篇 |
1983年 | 67篇 |
1982年 | 42篇 |
1981年 | 25篇 |
1980年 | 16篇 |
1979年 | 42篇 |
1978年 | 28篇 |
1977年 | 32篇 |
1976年 | 21篇 |
1975年 | 22篇 |
1974年 | 26篇 |
1973年 | 30篇 |
1970年 | 18篇 |
排序方式: 共有5932条查询结果,搜索用时 15 毫秒
101.
S Nisitani M Hosokawa M S Sasaki K Yasuoka H Naiki T Matsushita T Takeda 《Mutation research》1990,237(5-6):221-228
Age-related changes in the frequency of chromosome aberrations were examined using bone marrow cells of senescence-accelerated strains of mice (SAM). An accelerated senescence-prone strain, SAM-P/1, showed a striking increase in the frequency of chromosome aberrations, from age 3 to 8 months, whereas an accelerated senescence-resistant strain, SAM-R/1, at the same ages showed only a slight increase. Both these strains were derived from the same ancestral strain (AKR/J). The rate of increase of chromosome aberration frequency paralleled the advancement of senescence in both strains. These observations suggest that there are genetic factors which closely relate to chromosomal instability and acceleration of the senescence processes. 相似文献
102.
Kumon Keiro; Sasaki Jiro; Sejima Mototaro; Hayashi Yoshiyuki; Takeuchi Yasuyoshi 《Plant & cell physiology》1990,31(3):391-393
Accumulation of betacyanin in the peeled green epidermis fromthe stem of P. americana was induced by incubating the epidermisin Murashige and Skoog's medium, under light, and was promotedby the presence of kinetin. However, in the epidermal tissuewith cortex attached, the accumulation of betacyanin was inhibited. (Received March 27, 1989; Accepted January 24, 1990) 相似文献
103.
104.
105.
106.
K Ishibashi S Sasaki H Sakamoto Y Hoshino T Nakamura F Marumo 《Biochemical and biophysical research communications》1992,187(3):1454-1459
The renal expressions of the receptor gene (c-met) for hepatocyte growth factor (HGF) were examined in unilateral nephrectomy (UNX), renal ischemia or folic acid administration. The levels of c-met mRNA were increased rapidly in all rat models at 6h after the operations. On the other hand, the expression of c-met mRNA in a kidney cell line (MDCK cells) was down-regulated for 8 h after HGF addition, indicating that c-met mRNA induction in rat models may be independent of the stimulated production of HGF. The stimulated expression of c-met in these models suggest that HGF may play an important role in renal hypertrophy after UNX and regeneration after ischemic or nephrotoxic injury. 相似文献
107.
Intracellular pH values (pHi) of Xenopus oocytes were optically measured using a fluorescent dye, 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). The oocytes were loaded with dye by incubation with a membrane-permeable form (BCECF-AM). Mean pHi of the oocytes in pH 7.6 solution was 7.69. Increasing ambient pCO2 rapidly decreased pHi and estimated buffering power was 23.8 mM/pH unit. Changing ambient HCO3- from 5 to 30 mM did not alter pHi. After incubation in a Na(+)-free solution, Na+ addition to the bath rapidly increased pHi and this response was blocked by amiloride (ED50 2 microM). The addition of NH4Cl to the bath caused an initial transient increase in PHi followed by a secondary decrease. The secondary decrease was greatly inhibited by a histidine specific reagent, diethylpyrocarbonate. It was also slightly inhibited by ouabain, Ba2+ and furosemide, but not by amiloride. These data suggest that (1), fluorescence technique is applicable to PHi measurements of Xenopus oocytes; (2), Xenopus oocytes have an amiloride sensitive Na+/H(+)-exchange, and permeabilities to CO2, NH3, and NH+4. These observation may be useful in studying the relationship between pHi and oocytes development, and the expression of acid/base transporters in Xenopus oocytes. 相似文献
108.
H Koide Y Muto H Kasai K Kohri K Hoshi S Takahashi K Tsukumo T Sasaki T Oka T Miyake 《Biochimica et biophysica acta》1992,1120(3):257-261
The isoleucine-23 residue of human epidermal growth factor (hEGF) was substituted by a variety of amino acid residues and the receptor-binding activities of variant hEGFs were determined by the use of human KB cell. Tight receptor binding was found of variants with hydrophobic amino acid residues in position 23. The size of the isoleucine residue was nearly optimum for the receptor binding as compared with other hydrophobic residues. The structure analysis by two-dimensional nuclear magnetic resonance spectroscopy showed that the substitution at position 23 only slightly affected the tertiary structure of hEGF. These indicate that the side chain of isoleucine residue in position 23, which is exposed on the protein surface, directly binds to a hydrophobic pocket of the receptor. 相似文献
109.
Ken Sasaki Tohru Tanaka Yoshinori Nishizawa Mitsunori Hayashi 《Applied microbiology and biotechnology》1990,32(6):727-731
Summary For the production of a herbicide, 5-amino-levulinic acid (ALA), from anaerobic digestion liquor, the utilization of the photosynthetic bacterium, Rhodobacter sphaeroides was examined. This bacterium could produce ALA extracelularly from this liquor with the addition of levulinic acid (LA), an inhibitor of ALA dehydratase (ALAD), and glycine, a precursor of ALA biosynthesis in the Shemin pathway. Succinate (another precursor) addition was unnecessary for ALA production. When repeated additions of LA were made together with glycine ALA production was significantly enhanced. However, above three additions of LA, ALA production was not further enhanced. The maximum value of ALA production attained was 4.2 mM (0.63 g/ 1), which was over double that of other ALA producers such as Chlorella vulgaris. Propionic acid was predominantly utilized compared with other lower fatty acids, suggesting that this might be converted to ALA via succinyl-coenzyme A (CoA) in the methylmalonyl-CoA pathway.Offprint requests to: Y. Nishizawa 相似文献
110.
Y. Yamagata K. Sasaki O. Takaoka S. Sano K. Inomata K. Kanemitsu Y. Inoue I. Matsumoto 《Origins of life and evolution of the biosphere》1990,20(5):389-399
By heating an aqueous solution of aspartic acid and urea, carbamylaspartic acid is first formed and then the molecule is cyclized to dihydroorotic acid (DHO) with loss of water. Irradiation of an aqueous solution of DHO with a tungsten lamp yields orotic acid by photo-dehydrogenation of the molecule. This pathway of orotic acid formation is quite similar to that of biosynthesis of the molecule. 相似文献