全文获取类型
收费全文 | 8217篇 |
免费 | 408篇 |
国内免费 | 1篇 |
出版年
2023年 | 35篇 |
2022年 | 32篇 |
2021年 | 81篇 |
2020年 | 105篇 |
2019年 | 126篇 |
2018年 | 299篇 |
2017年 | 262篇 |
2016年 | 348篇 |
2015年 | 294篇 |
2014年 | 400篇 |
2013年 | 549篇 |
2012年 | 482篇 |
2011年 | 643篇 |
2010年 | 366篇 |
2009年 | 240篇 |
2008年 | 447篇 |
2007年 | 503篇 |
2006年 | 527篇 |
2005年 | 441篇 |
2004年 | 383篇 |
2003年 | 398篇 |
2002年 | 330篇 |
2001年 | 201篇 |
2000年 | 178篇 |
1999年 | 124篇 |
1998年 | 71篇 |
1997年 | 24篇 |
1996年 | 18篇 |
1995年 | 21篇 |
1994年 | 21篇 |
1993年 | 25篇 |
1992年 | 21篇 |
1991年 | 27篇 |
1990年 | 20篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 28篇 |
1986年 | 24篇 |
1985年 | 38篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1979年 | 28篇 |
1978年 | 23篇 |
1977年 | 25篇 |
1972年 | 17篇 |
1953年 | 18篇 |
1952年 | 40篇 |
1887年 | 14篇 |
排序方式: 共有8626条查询结果,搜索用时 31 毫秒
1.
2.
3.
Judyta Kruk Irena Baranowska Bogusaw Buszewski Sylwia Bajkacz Bartosz Kowalski Magdalena Ligor 《Chirality》2019,31(2):138-149
Plant material is a rich source of valuable compounds such as flavanones. Their different forms influence bioavailability and biological activity, causing problems with the selection of plant material for specific purposes. The purpose of this research was to determine selected flavanone (eriodictyol, naringenin, liquiritigenin, and hesperetin) enantiomer contents in free form and bonded to glycosides by an RP‐UHPLC‐ESI‐MS/MS method. Different parts (stems, leaves, and flowers) of goldenrod (Solidago virgaurea L.), lucerne (Medicago sativa L.), and phacelia (Phacelia tanacetifolia Benth.) were used. The highest content of eriodictyol was found in goldenrod flowers (13.1 μg/g), where it occurred mainly as the (S)‐enantiomer, and the greatest proportion of the total amount was bonded to glycosides. The richest source of naringenin was found to be lucerne leaves (4.7 μg/g), where it was mainly bonded to glycosides and with the (S)‐enantiomer as the dominant form. Liquiritigenin was determined only in lucerne, where the flowers contained the highest amount (1.2 μg/g), with the (R)‐enantiomer as dominant aglycone form and the (S)‐enantiomer as the dominant glycosylated form. The highest hesperetin content was determined in phacelia leaves (0.38 μg/g), where it was present in the form of a glycoside and only as the (S)‐enantiomer. A comparison of the different analyte forms occurring in different plant parts was performed for the first time. 相似文献
4.
The majority of terrestrial biomass is wood, but the elemental composition of its potential consumers, xylophages, differs hugely from that of wood. This causes a severe nutritional imbalance. We studied the stoichiometric relationships of 11 elements (C, N, P, K, Ca, Mg, Fe, Zn, Mn, Cu, Na) in three species of pine-xylem-feeding insects, Stictoleptura rubra, Arhopalus rusticus (Coleoptera, Cerambycidae) and Chalcophora mariana (Coleoptera, Buprestidae), to elucidate their mechanisms of tissue growth and to match their life histories to their dietary constraints. These beetles do not differ from other Coleoptera in their absolute elemental compositions, which are approximately 1000 (N), 100 (P, Cu) and 50 (K, Na) times higher than in dead but undecayed pine wood. This discrepancy diminishes along the wood decay gradient, but the elemental concentrations remain higher by an order of magnitude in beetles than in highly decayed wood. Numerical simulation of the life history of S. rubra shows that feeding on nutrient-poor undecayed wood would extend its development time to implausible values, whereas feeding on highly decomposed wood (heavily infected with fungi) would barely balance its nutritional budget during the long development period of this species. The changes in stoichiometry indicate that the relative change in the nutrient levels in decaying wood cannot be attributed solely to carbon loss resulting from decomposer respiration: the action of fungi substantially enriches the decaying wood with nutritional elements imported from the outside of the system, making it a suitable food for wood-eating invertebrates. 相似文献
5.
A Dutour P Giraud C Kowalski L Ouafik P Salers V Strbak C Oliver 《Biochemical and biophysical research communications》1987,146(1):354-360
The rapid changes in TRH levels in the rat pancreas during the neonatal period make this organ an interesting model for the study of the regulation of TRH biosynthesis. Pancreatic RNAs were isolated by the guanidinium thiocyanate method and layered onto CsCl cushion. Northern blot preparations were hybridized with 32P labeled TRH cDNA probe. Pancreatic TRH mRNA was first detected in 19-day old fetuses and reached the highest level on day 0, then decreased, being barely detectable 14 days after birth. The neonatal injection of streptozotocin induced a dramatic drop of TRH mRNA levels 24 hours later. This result suggests that the peculiar evolution of TRH level in pancreas is partly due to the evolution of the expression of the TRH gene. 相似文献
6.
Rafał Krętowski Anna Stypułkowska Marzanna Cechowska-Pasko 《Molecular and cellular biochemistry》2015,398(1-2):165-173
The inhibition of the 26S proteasome evokes endoplasmic reticulum stress, which has been shown to be implicated in the antitumoral effects of proteasome inhibitors. The cellular and molecular effects of the proteasome inhibitor—bortezomib—on human colon cancer cells are as yet poorly characterized. Bortezomib selectively induces apoptosis in some cancer cells. However, the nature of its selectivity remains unknown. Previously, we demonstrated that, in contrast to normal fibroblasts, bortezomib treatment evoked strong effect on apoptosis of breast cancer cells incubated in hypoxic and normoxic conditions. The study presented here provides novel information on the cellular effects of bortezomib in DLD-1 colon cancer cells line. We observe twofold higher percentage of apoptotic cells incubated for 48 h with 25 and 50 nmol/l of bortezomib in hypoxic conditions and four-, fivefold increase in normoxic conditions in comparison to control cells, incubated without bortezomib. It is of interest that bortezomib evokes strong effect on necrosis of DLD-1 colon cancer cell line. We observe the sixfold increase in necrosis of DLD-1 cells incubated with 25 or 50 nmol/l of bortezomib for 48 h in hypoxia and fourfold increase in normoxic conditions in comparison to adequate controls. We suggest that bortezomib may be candidates for further evaluation as chemotherapeutic agents for human colon cancer. 相似文献
7.
8.
Jacek Kęsy Beata Maciejewska Magdalena Sowa Magdalena Szumilak Krzysztof Kawałowski Maja Borzuchowska Jan Kopcewicz 《Plant Growth Regulation》2008,55(1):43-50
It has been shown that both IAA and ethylene application inhibit flower induction in the short-day plant Pharbitis nil. However application of IAA has elevated ethylene production in this plant, as well. Strong enhancement of ethylene production
is also correlated with the night-break effect, which completely inhibits flowering. In order to determine what the role of
IAA and ethylene is in the photoperiodic flower induction in Pharbitis nil, we measured changes in their levels during inductive and non-inductive photoperiods, and the effects of ethylene biosynthesis
and action inhibitors on inhibition of flowering by IAA. Our results have shown that the inhibitory effect of IAA on Pharbitis nil flowering is not physiological but is connected with its effect on ethylene biosynthesis. 相似文献
9.
10.