全文获取类型
收费全文 | 2495篇 |
免费 | 116篇 |
国内免费 | 7篇 |
出版年
2022年 | 16篇 |
2021年 | 26篇 |
2020年 | 13篇 |
2019年 | 18篇 |
2018年 | 28篇 |
2017年 | 22篇 |
2016年 | 45篇 |
2015年 | 86篇 |
2014年 | 85篇 |
2013年 | 152篇 |
2012年 | 150篇 |
2011年 | 131篇 |
2010年 | 73篇 |
2009年 | 78篇 |
2008年 | 146篇 |
2007年 | 164篇 |
2006年 | 132篇 |
2005年 | 159篇 |
2004年 | 159篇 |
2003年 | 140篇 |
2002年 | 142篇 |
2001年 | 44篇 |
2000年 | 61篇 |
1999年 | 47篇 |
1998年 | 39篇 |
1997年 | 28篇 |
1996年 | 29篇 |
1995年 | 28篇 |
1994年 | 16篇 |
1993年 | 18篇 |
1992年 | 36篇 |
1991年 | 37篇 |
1990年 | 25篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 19篇 |
1986年 | 29篇 |
1985年 | 13篇 |
1984年 | 17篇 |
1983年 | 19篇 |
1982年 | 11篇 |
1981年 | 24篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 6篇 |
排序方式: 共有2618条查询结果,搜索用时 46 毫秒
1.
Enzymes are remarkable molecules which make metabolism possible. Their processing powers are considerable for not only are they catalysts they also contribute to information processing, integration, coherence and memory in the cell. This complex of attributes suggests that a complementary perspective to enzyme nature and activity is needed related to what enzymes and verbs have in common. The value of this kind of thinking is that it shifts the focus from objects and mechanisms to processes and information. In order to support this idea a number of features which enzymes and verbs share are discussed including, context-dependence, occurrence, cases, voice, mood and glue/integrative capacities. The paper concludes with some reflections on the utility of a view of enzymes as verbs. 相似文献
2.
T Maoka A Arai M Shimizu T Matsuno 《Comparative biochemistry and physiology. B, Comparative biochemistry》1986,83(1):121-124
Racemic mixtures of (3RS, 3'RS)-zeaxanthin were separated into the three optical isomers, (3R, 3'R)-zeaxanthin (1), (3R,3'S;meso)-zeaxanthin (2) and (3S,3'S)-zeaxanthin (3), by converting to their corresponding dibenzoates and by using HPLC on an optical resolution column Sumipax OA-2000. According to this procedure, it has been shown that only (1) is isolated from higher plants, shellfish, starfish, sea squirt, sea cucumber and then examined; on the other hand (1), (2) and (3) are isolated from zeaxanthin fraction of shrimp, fish and turtle examined. This is the first isolation of enantiomeric and meso-zeaxanthin in nature. 相似文献
3.
4.
Junichi Ishihara Nagahiro Saijo Yasutsuna Sasaki Hidehiko Nakano Akira Ozaki Hidenobu Takahashi Masanori Sakurai Kazuhiko Nakagawa Masaaki Iigo Fumihiko Kanzawa Akio Hoshi Weon Seon Hong James R. Jett Terumi Takahashi 《Cancer immunology, immunotherapy : CII》1987,24(3):185-189
Summary The antitumor effect of recombinant human tumor necrosis factor (rH-TNF) on two clones of rat fibrosarcoma with different metastatic potential to lymph nodes was examined. The colony formation of clone A, which has high metastatic potential, was completely inhibited by continuous exposure to rH-TNF at 50 U/ml. In contrast, colony formation of clone G, which has low metastatic potential, was not inhibited by high concentrations of rH-TNF (10,000 U/ml). The inhibitory effect of rH-TNF on colony formation by clone A was also observed with a 1-h exposure to rH-TNF. This effect was time and concentration dependent, as determined by the colony assay, 3H-thymidine uptake assay, and 51Cr-release assay. 3H-thymidine and 3H-uridine uptake per cell of clone A exposed to rH-TNF was not decreased. This suggests that the mechanisms of the antitumor effect of rH-TNF were not due to inhibition of DNA and RNA synthesis of tumor cells. In vivo growth and lymph node metastases of clone A inoculated i.p. to Donryu strain rats were completely suppressed by 14 consecutive i.p. injections of 105 or 106 U/kg per day of rH-TNF. On the other hand the growth of clone G was not influenced by rH-TNF administration. 相似文献
5.
Glutamine synthetase and glutaminase activities in a series of hepatoma cells of human and rat origins were determined for comparison with normal liver tissues. Marked decrease in glutamine synthetase activity was observed in the tumor cells. Phosphate-dependent and phosphate-independent glutaminase activities were increased compared with those from normal liver tissues. Well coupled mitochondria were isolated from HuH 13 line of human hepatoma cells and human liver. Oxypolarographic tests showed that glutamine oxidation was prominent in the tumor mitochondria, while mitochondria from the liver showed a feeble glutamine oxidation. Glutamine oxidation was inhibited by prior incubation of the mitochondria with DON (6-diazo-5-oxo-L-norleucine), which inhibited mitochondrial glutaminase. These results indicate that the product of glutamine hydrolysis, glutamate, is catabolized in the tumor mitochondria to supply ATP. 相似文献
6.
Summary In an attempt to reveal the role of antigen-laden marginal metallophil (MM) and other macrophages in the intrasplenic immune response of a specific B-cell lineage to a thymus-independent type-2 antigen (Ficoll conjugated with fluorescein isothiocyanate), simultaneous immuno-histological observations of the involved cells were performed in the rat. By newly established methods of double or triple immunostainings, time-kinetics of the following parameters were studied and compared: (1) the antigen, (2) the specific antibody-forming cells (AFC) directed to the fluorescein-isothiocyanate determinant, (3) proliferating cells labeled with 5-bromo-2-deoxyuridine (BrdU), and (4) macrophage subpopulations recognized by monoclonal antibodies (ED2 and ED3). The antigen localized stably not only in the marginal-zone macrophages but also in the MM except around the follicular area. The increase of BrdU-positive cells was observed from day 2 up to day 4 after antigen injection mostly in the periphery of the periarterial lymphoid sheath (outer PALS), which indicated antigen-induced proliferation. As a novel finding, the majority of AFC, both BrdU-positive and -negative, were either closely associated with the antigen-laden MM, or forming cell clusters with ED2-positive macrophages in the outer PALS. In contrast, there were very few AFC in juxtaposition to antigen-free MM in the follicular area or the antigen-laden marginal zone macrophages. The results led to the proposal of a hypothesis that the antigen-laden MM together with ED2-positive macrophages constitute an immunoproliferative microenvironment for the plasmacellular reaction by accumulating the antigen-specific B-cell lineage and promoting these cells to differentiate into the AFC and to proliferate in the outer PALS.Abbreviations
AFC
specific antibody-forming cells
- BrdU
5-bromo-2-deoxyuridine
- Fic-F
FITC-conjugated Ficoll
- FITC
fluorescein isothiocyanate
- HRP
horseradish peroxidase
- MM
marginal metallophils
- MZ
marginal zone
- PALS
periarterial lymphoid sheath
- PBS
phosphate-buffered saline
- TI2
thymus-independent type-2 相似文献
7.
8.
Furuichi Y Oogida T Mitsui C Matsuno M Takahashi T 《The Journal of nutritional biochemistry》1990,1(4):196-199
Glucose was combined covalently with the epsilon-amino groups of lysyl residues of bovine casein in the presence of sodium cyanoborohydride as a reducing reagent by reductive alkylation, forming stable secondary amine linkages. Solubility characteristics and nutritional values of the neoglycoprotein were examined. The degree of modification (%) of the glucosylated casein was 82.5. Solubility of the modified casein was increased by the attachment of glucose. The modification did not disturb the digestion of casein by pepsin or trypsin. Rat feeding experiments using 10% protein diets demonstrated that the protein efficiency ratio (PER) of the modified casein was 0.35 +/- 0.33 compared with 2.99 +/- 0.29 for the unmodified casein. When the modified casein was supplemented with L-lysine to equal the level of total lysine of unmodified casein, the PER value was increased to 2.21 +/- 0.29. Nitrogen balance experiments showed that the modified casein was digested completely. On the other hand, biological value and net protein utilization of the modified protein were shown to be considerably lower than those of the unmodified casein. 相似文献
9.
H+-translocating ATPase and pyrophosphatase (PPase) associatedwith the tonoplast of Chara corallina were isolated with theaid of a perfusion technique, and the effects of ions on theiractivities were studied. All the alkali metal cations testedstimulated the ATPase and ATPdependent H+ pumping activitiesonly by 10 to 40%. Anions, on the other hand, strongly affectedthe activities. Potassium salts of Cl- and Br- stimulated them,while F- and NO3- inhibited them. By contrast, the H+-translocatingPPase was insensitive to anions but sensitive to cations. Theorder of cation stimulation was Rb+=K+>Cs+>Na+=Li+>choline+.NO3- (50 mil), thought to be a specific inhibitor of the tonoplast-typeH+-ATPase, inhibited the ATPdependent H+ pumping almost completelybut the ATPase activity by only about 50%. Na+ inhibited thePP1-dependent H+ pumping (I5O=5OmM) in the presence of 50 mMKCl but not the ATP-dependent one. The PPase was more sensitiveto F- (I50=400µM) than the ATPase. Both the H+-ATPaseand the H+-PPase required Mg2+ for their activities, althoughan excess was inhibitory to both. The different sensitivitiesof the PP1-dependent and the ATP-dependent H+- pumping enzymesto ions correspond to the tonoplast enzymes of higher plantsand may be used as "markers" to distinguish between these enzymesin characean cells (Received October 2, 1987; Accepted May 18, 1988) 相似文献
10.
Kiyoshi Takahashi Katsuya Miyatani Hiroyuki Yanai Ho Jong Jeon Kotaro Fujiwara Tadashi Yoshino Kazuhiko Hayashi Tadaatsu Akagi Ken Tsutsui Koichi Mizobuchi 《Virchows Archiv. B, Cell pathology including molecular pathology》1992,62(1):105-113
Monocytic leukemia (MoL) cells were obtained from the peripheral blood of a patient in whom the leukemic cells infiltrating
various lymphoreticular organs exhibited features intermediate between interdigitating reticulum cells (IDC) and ordinary
phagocytic macrophages, whereas the leukemic cells in the peripheral blood were essentially monocytic and lacked such features.
Peripheral blood CD4+ T-cells were established as an interleukin-2-dependent T-cell line. When the MoL cells were exposed
for a few days to conditioned medium from the T-cell line, they extended several dendritic cytoplasmic projections and became
intensely positive for HLA-DR antigen, cytoplasmic S-100β protein, and CD1 antigen. Functionally, the conditioned medium significantly
down-regulated Fc-mediated and Fc-independent phagocytic activities, and the levels of lysosomal enzymes such as lysozyme
and nonspecific esterase in the MoL cells. Moreover, the conditioned medium significantly up-regulated the accessory cell
function of the MoL cells as measured by the primary allogenic mixed leukocyte reaction (MLR). Furthermore, the conditioned
medium significantly down-regulated the expression of CD14 antigen.
Biochemical analysis indicated that the factor responsible for these changes is a protein which is distinct from known human
cytokines and whose molecular weight is approximately 31 kDa. These findings suggest that IDC are closely related the monocytic
lineage and that helper T-cells play an important role in constructing the microenvironment of T-lymphoid tissues which is
necessary for the differentiation and maturation of IDC. 相似文献